But then I think I'd expect using the mood browser to overwrite what I'd typed in, and vice versa. Having autocompletion would be nice, but I do use custom moods and pick 'standard' moods to have as the icon fairly often and would really hate to lose that.

A check box, maybe? That way you could have the angry icon and the text "happy" even though right now that's not possible (if your custom mood matches something, it's the same as picking from the dropdown), or the angry icon and the text "really exceptionally angry" or whatever.