I would report it as a bug, but as a workaround, have you tried wrapping the calls that generate this in their own autorelease pool? Though it shouldn't be necessary - callbacks should be happening on the main thread (the thread from which they are called) unless documented otherwise, and the main thread always has an autorelease pool.
Or, are you perhaps, setting the callback from within a thread? In that case, the callback will probably function on that thread, and if your thread method has ended and released its autorelease pool, then that would explain the problem. You can fix that problem by calling a method on the main thread to set the callback.
But if you're doing everything in the main thread, then I'd definitely file it as a bug, and try wrapping the calls to like this as a workaround:
Code:
NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
...code that generates leak message
[pool release];
