I've had a chance to focus on this again - and I think I was getting fooled. Neither the Auto-Lock nor the manual locking knocks me out of the game. It seems to simply be a question of how many memory large other Apps that I run before I try to run BA again.

I've found that if I get busy during MP games and my IPad "auto-locks" (the screen goes blank), when I reactivate the BA App - I'm no longer in the game, but at the main BA Menu. I must go back to multiplayer > reconnect to the server >and redownload the game (having lost everything I had ...