Yep! Game data is synched by default, I believe..
For the record, we were able to circumvent the problem by uninstalling the game and then reinstalling.
I'm having the same issue-- tried to start the game during the update process (I didn't notice it was trying to update) and rebooted the box before the update completed. Upon reboot, I noticed the update and it finished, but game will not launch. Game will sometimes get to the menu screen and play the notification sound before freezing and then crashing out back to the xbox menu.
I'm new to Mojang's Jira setup, but I'm surprised that after two weeks, there's apparently no acknowledgement from Mojang about the issue. Was there anyone at the company who looked at the issue? If they know that reinstalling would fix it, could they post that as a workaround or solution? Guess I assumed there would be more action on their part...