Cocoa bindings causing dealloc to not be called?

In tracking down a bug in ReceiptWallet, I discovered some end (at least to me) odd behavior. ReceiptWallet is an NSDocument based application. When the document is closed, is should call dealloc to release its memory. This wasn’t happening. It appears that some things in my code prevented dealloc from being called; I had to unbind some Cocoa bindings (not all of them, however):

	[_receiptsArrayController unbind:@"selectionIndexes"];
	[photoSizeSlider unbind:@"value"];
	[self unbind:@"currentSelectedIndexes"];

and then I had to remove some observers:

	[collectionsTreeController removeObserver:self forKeyPath:@"selectionIndexPaths"];
	[userDefaultsController removeObserver:self
		forKeyPath:@"values.Show Details With Thumbnails"];

and to top it off, I had to set the view on a toolbar item (a search item) to nil:

	extern NSString *SearchToolbarItemIdentifier;
	NSArray *items = [[[self window] toolbar] items];
	NSEnumerator *itemEnumr = [items objectEnumerator];
	NSToolbarItem *item = nil;
	while (item = [itemEnumr nextObject])
	{
		if ([[item itemIdentifier] isEqualToString:SearchToolbarItemIdentifier])
		{
			[item setView:nil];
			break;
		}
	}

I can understand removing the observer for user defaults, but the bindings have me confused as the bindings are for items that should get released anyway. I’m probably missing something simple, but I’m glad I figured this one out.