XCode 7 Instruments - Why is this leaking? - objective-c

Question

I fell into a strange thing: Why is the following code fragment producting leaks (attrDefault not released)? (assume, 'font' has been defined before and self.text refers to an NSString*):
{
NSStringDrawingContext* context = [[NSStringDrawingContext alloc] init];
NSDictionary* attrDefault = #{ NSForegroundColorAttributeName : [UIColor blackColor],
NSBackgroundColorAttributeName : [UIColor clearColor],
NSFontAttributeName : font,
};
frame.size.height = 1024;
CGRect bounding = [self.text boundingRectWithSize:frame.size
options:NSStringDrawingUsesLineFragmentOrigin|NSStringDrawingUsesFontLeading|NSStringDrawingUsesDeviceMetrics
attributes:attrDefault context:context];
frame.size.height = bounding.size.height;
[context release];
}
Any idea?
Update:
Surprisingly, if the same code is embedded into an #autoreleasepool statement, the leaks are gone.
#autoreleasepool {
NSStringDrawingContext* context = [[NSStringDrawingContext alloc] init];
NSDictionary* attrDefault = #{ NSForegroundColorAttributeName : [UIColor blackColor],
NSBackgroundColorAttributeName : [UIColor clearColor],
NSFontAttributeName : font,
};
frame.size.height = 1024;
NSString* text = self.text;
CGRect bounding = [text boundingRectWithSize:frame.size
options:NSStringDrawingUsesLineFragmentOrigin|NSStringDrawingUsesFontLeading|NSStringDrawingUsesDeviceMetrics
attributes:attrDefault context:context];
frame.size.height = bounding.size.height;
[context release]; }
I did not get any leaks with XCode 6, by the way.
This is pretty strange, as I use NSDictionary constructors ( #{....} ) at a lot of locations in my code and the DO NOT produce any leaks.
Anybody with similiar experience?