Me and my sister recently both got this on the 360, we have played through it twice online, once on fixed worlds and once on random worlds. Both times as soon as we collected the last Rocket ship piece immediately a message pops up saying 'session ended' and we are kicked out without getting to do the playable ending, kinda soul destroying after spending upwards of 2 hours to get there.

It seems strange this part of the game is just not possible online, I haven't done it in single player yet but assume it would let you actually properly complete the game.

YA did so with my brother just now... outraged. Want my money back.. doesn't even allow achievements in CO-OP... utter disgrace. I feel cheated from this classic. What a waste of time.