diff --git a/AppKit/CPDragServer.j b/AppKit/CPDragServer.j
index 9d3344b09..bc67ee490 100644
--- a/AppKit/CPDragServer.j
+++ b/AppKit/CPDragServer.j
@@ -270,10 +270,10 @@ var CPDraggingSource_draggedImage_movedTo_          = 1 << 0,
             {
                 if ([scrollView hasVerticalScroller])
                 {
-                    if (eventLocation.y < CGRectGetMinY(insetBounds))
-                        deltaY = CGRectGetMinY(insetBounds) - eventLocation.y;
-                    else if (eventLocation.y > CGRectGetMaxY(insetBounds))
-                        deltaY = CGRectGetMaxY(insetBounds) - eventLocation.y;
+                    if (eventLocation.y < _CGRectGetMinY(insetBounds))
+                        deltaY = _CGRectGetMinY(insetBounds) - eventLocation.y;
+                    else if (eventLocation.y > _CGRectGetMaxY(insetBounds))
+                        deltaY = _CGRectGetMaxY(insetBounds) - eventLocation.y;
                     if (deltaY < -insetBounds.size.height)
                         deltaY = -insetBounds.size.height;
                     if (deltaY > insetBounds.size.height)
@@ -282,17 +282,21 @@ var CPDraggingSource_draggedImage_movedTo_          = 1 << 0,
 
                 if ([scrollView hasHorizontalScroller])
                 {
-                    if (eventLocation.x < CGRectGetMinX(insetBounds))
-                        deltaX = CGRectGetMinX(insetBounds) - eventLocation.x;
-                    else if (eventLocation.x > CGRectGetMaxX(insetBounds))
-                        deltaX = CGRectGetMaxX(insetBounds) - eventLocation.x;
+                    if (eventLocation.x < _CGRectGetMinX(insetBounds))
+                        deltaX = _CGRectGetMinX(insetBounds) - eventLocation.x;
+                    else if (eventLocation.x > _CGRectGetMaxX(insetBounds))
+                        deltaX = _CGRectGetMaxX(insetBounds) - eventLocation.x;
                     if (deltaX < -insetBounds.size.width)
                         deltaX = -insetBounds.size.width;
                     if (deltaX > insetBounds.size.width)
                         deltaX = insetBounds.size.width;
                 }
 
-                [contentView scrollToPoint:CGPointMake(bounds.origin.x - deltaX, bounds.origin.y - deltaY)];
+                var scrollPoint = _CGPointMake(bounds.origin.x - deltaX, bounds.origin.y - deltaY);
+
+                [contentView scrollToPoint:scrollPoint];
+                [[scrollView _headerView] scrollPoint:scrollPoint];
+
             }
         }
     }
diff --git a/Foundation/CPArray/CPMutableArray.j b/Foundation/CPArray/CPMutableArray.j
index bf0874224..e9588dd51 100644
--- a/Foundation/CPArray/CPMutableArray.j
+++ b/Foundation/CPArray/CPMutableArray.j
@@ -332,7 +332,7 @@
     [self replaceObjectAtIndex:otherIndex withObject:temporary];
 }
 
-- (CPArray)sortUsingDescriptors:(CPArray)descriptors
+- (void)sortUsingDescriptors:(CPArray)descriptors
 {
     [self sortUsingFunction:compareObjectsUsingDescriptors context:descriptors];
 }
diff --git a/Foundation/CPKeyValueObserving.j b/Foundation/CPKeyValueObserving.j
index fbac24c09..ee72d91fc 100644
--- a/Foundation/CPKeyValueObserving.j
+++ b/Foundation/CPKeyValueObserving.j
@@ -678,6 +678,14 @@ var kvoNewAndOld        = CPKeyValueObservingOptionNew | CPKeyValueObservingOpti
 {
     var observers = _observersForKey[aPath];
 
+    if (!observers)
+    {
+        CPLog.warn(@"Cannot remove an observer %@ for the key path \"%@\" from %@ because it is not registered as an observer.",
+            _targetObject, aPath, anObserver);
+
+        return;
+    }
+
     if (aPath.indexOf('.') != CPNotFound)
     {
         var forwarder = [observers objectForKey:[anObserver UID]].forwarder;
diff --git a/Foundation/CPURL.j b/Foundation/CPURL.j
index 1b60010a0..810677c7e 100644
--- a/Foundation/CPURL.j
+++ b/Foundation/CPURL.j
@@ -227,7 +227,7 @@ CPURLCustomIconKey                  = @"CPURLCustomIconKey";
     return self.setResourcePropertyForKey(aKey, anObject);
 }
 
-- (CPString)staticResourceData
+- (CPData)staticResourceData
 {
     return self.staticResourceData();
 }
diff --git a/Tests/AppKit/CPKeyValueObservingTest.j b/Tests/AppKit/CPKeyValueObservingTest.j
deleted file mode 100644
index 67e3cd07b..000000000
--- a/Tests/AppKit/CPKeyValueObservingTest.j
+++ /dev/null
@@ -1,106 +0,0 @@
-@import <Foundation/CPKeyValueObserving.j>
-
-@implementation CPKeyValueObservingTest : OJTestCase
-{
-    CPString      _lastKeyPath;
-    id            _lastObject;
-    CPDictionary  _lastChange;
-    id            _lastContext;
-}
-
-- (void)setup
-{
-  _lastKeyPath = _lastObject = _lastChange = _lastContext = nil;
-}
-
-- (void)testInitialObserving
-{
-    var tester = [ObservingTester testerWithCheese:@"CHEESE!"];
-    [tester addObserver:self forKeyPath:@"cheese" options:CPKeyValueObservingOptionNew | CPKeyValueObservingOptionInitial context:nil];
-
-    [self assert:@"cheese" equals:_lastKeyPath];
-    [self assert:tester equals:_lastObject];
-    [self assert:[CPDictionary dictionaryWithObject:@"CHEESE!" forKey:CPKeyValueChangeNewKey] equals:_lastChange];
-    [self assert:nil equals:_lastContext];
-}
-
-- (void)observeValueForKeyPath:(CPString)aKeyPath
-                      ofObject:(id)anObject
-                        change:(CPDictionary)aChange
-                       context:(id)aContext
-{
-    _lastKeyPath = aKeyPath;
-    _lastObject  = anObject;
-    _lastChange  = aChange;
-    _lastContext = aContext;
-}
-
-- (void)testSendNotificationsForDependantKeyPaths
-{
-    var observingTester = [ObservingTester testerWithCheese:@"cheese"],
-        dependantKeyPathTester = [DependantKeyPathsTester testerWithObservingTester:observingTester];
-
-    [dependantKeyPathTester addObserver:self forKeyPath:@"observedCheese" options:CPKeyValueObservingOptionNew context:nil];
-    [observingTester setCheese:@"changed cheese"];
-
-    [self assert:@"observedCheese" equals:_lastKeyPath]
-    [self assert:dependantKeyPathTester equals:_lastObject];
-}
-
-@end
-
-@implementation ObservingTester : CPObject
-{
-    id cheese;
-}
-
-+ (id)testerWithCheese:(id)aCheese
-{
-    var tester = [[self alloc] init];
-    [tester setCheese:aCheese];
-    return tester;
-}
-
-- (void)setCheese:(id)aCheese
-{
-    cheese = aCheese;
-}
-
-- (id)cheese
-{
-    return cheese;
-}
-
-@end
-
-@implementation DependantKeyPathsTester: CPObject
-{
-    ObservingTester                 _observingTester @accessors(property=observingTester);
-}
-
-+ (CPSet)keyPathsForValuesAffectingObservedCheese
-{
-    return [CPSet setWithObjects:@"observingTester.cheese"];
-}
-
-+ (id)testerWithObservingTester:(ObservingTester)theObservingTester
-{
-    return [[self alloc] initWithObservingTester:theObservingTester];
-}
-
-- (id)initWithObservingTester:(ObservingTester)theObservingTester
-{
-    if (self = [super init])
-    {
-        _observingTester = theObservingTester;
-    }
-
-    return self;
-}
-
-- (CPString)observedCheese
-{
-    return [[self observingTester] cheese];
-}
-
-@end
diff --git a/Tests/Foundation/CPKeyValueObservingTest.j b/Tests/Foundation/CPKeyValueObservingTest.j
index 5d43fc8da..2d409618f 100644
--- a/Tests/Foundation/CPKeyValueObservingTest.j
+++ b/Tests/Foundation/CPKeyValueObservingTest.j
@@ -22,6 +22,45 @@
     return [theClass new];
 }
 
+- (void)setup
+{
+  _lastKeyPath = _lastObject = _lastChange = _lastContext = nil;
+}
+
+- (void)testInitialObserving
+{
+    var tester = [ObservingTester testerWithCheese:@"CHEESE!"];
+    [tester addObserver:self forKeyPath:@"cheese" options:CPKeyValueObservingOptionNew | CPKeyValueObservingOptionInitial context:nil];
+
+    [self assert:@"cheese" equals:_lastKeyPath];
+    [self assert:tester equals:_lastObject];
+    [self assert:[CPDictionary dictionaryWithObject:@"CHEESE!" forKey:CPKeyValueChangeNewKey] equals:_lastChange];
+    [self assert:nil equals:_lastContext];
+}
+
+- (void)observeValueForKeyPath:(CPString)aKeyPath
+                      ofObject:(id)anObject
+                        change:(CPDictionary)aChange
+                       context:(id)aContext
+{
+    _lastKeyPath = aKeyPath;
+    _lastObject  = anObject;
+    _lastChange  = aChange;
+    _lastContext = aContext;
+}
+
+- (void)testSendNotificationsForDependantKeyPaths
+{
+    var observingTester = [ObservingTester testerWithCheese:@"cheese"],
+        dependantKeyPathTester = [DependantKeyPathsTester testerWithObservingTester:observingTester];
+
+    [dependantKeyPathTester addObserver:self forKeyPath:@"observedCheese" options:CPKeyValueObservingOptionNew context:nil];
+    [observingTester setCheese:@"changed cheese"];
+
+    [self assert:@"observedCheese" equals:_lastKeyPath]
+    [self assert:dependantKeyPathTester equals:_lastObject];
+}
+
 - (void)testOnlyInsertObject_AtKeyIndex_Implemented
 {
     var insertSelector = @selector(insertObject:inObjectsAtIndex:),
@@ -155,3 +194,59 @@
 }
 
 @end
+
+@implementation ObservingTester : CPObject
+{
+    id cheese;
+}
+
++ (id)testerWithCheese:(id)aCheese
+{
+    var tester = [[self alloc] init];
+    [tester setCheese:aCheese];
+    return tester;
+}
+
+- (void)setCheese:(id)aCheese
+{
+    cheese = aCheese;
+}
+
+- (id)cheese
+{
+    return cheese;
+}
+
+@end
+
+@implementation DependantKeyPathsTester: CPObject
+{
+    ObservingTester                 _observingTester @accessors(property=observingTester);
+}
+
++ (CPSet)keyPathsForValuesAffectingObservedCheese
+{
+    return [CPSet setWithObjects:@"observingTester.cheese"];
+}
+
++ (id)testerWithObservingTester:(ObservingTester)theObservingTester
+{
+    return [[self alloc] initWithObservingTester:theObservingTester];
+}
+
+- (id)initWithObservingTester:(ObservingTester)theObservingTester
+{
+    if (self = [super init])
+    {
+        _observingTester = theObservingTester;
+    }
+
+    return self;
+}
+
+- (CPString)observedCheese
+{
+    return [[self observingTester] cheese];
+}
+
+@end