Thanks for reporting this bug. I experienced it myself a few times already and other users did so, too. Not yet sure what's the cause for it, but its on my list. Will be fixed in the next release.
Well, by now it is really annoying to wait until the game "crashes" everytime i end a game and wanna start a new one, blackscreen, and it is not gone by simply end app and start again.. i have to wait sometimes hours until is works again.. HTC One XL
I'm really sorry for this issue. It's on my top priority list for the next release. Until now I thought this is just annoying, but there's a workaround by restarting the app. I didn't think of that on older Android versions it is not possible to close a specific app. :-( @Cupido Nice workaround for android devices that do not allow to force close a specific app!