not really a bug, but more of a suggestion. i've multiple times accidentally pushed backspace while deckbuilding and had it take me "back" to the main forum. of course, then my deck was not saved, and had to be completely restarted. maybe if there is an unsaved deck being built, if you try to leave, could it stop you and say "your deck is not saved, are you sure you want to leave without saving?"
don't know if this is possible or easy to do, just a thought.