A beginner's mistake:

.h @interface { NSMutableDictionary myDict; } @property (nonatomic, retain) NSMutableDictionary myDict;

myDict = [[NSMutableDictionary dictionaryWithObjectsAndKeys: ..., ..., nil] retain];

If NSMutableDictionary is created with NSMutableDictionary dictionaryWithObjectsAndKeys, and it should be retained, it has to been sent a retain message explicitly.

No alloc, no init, no retain...