I thought it was just bad luck, but the exact same thing happened later when I went to Magmar. I didn't delete the old Magmar world, however, so when the game crashed and rolled back, I was still in the Magmar part of that world. I thought I would just try again, but going back through the portal resulted in this error:

(Destroying the portal, rebuilding it and entering results in Jack going to a newly generated Terra world, without the Magmar portal.)
It looks like it's not deleting the connected worlds when I delete the adventure world, but rather just Terra. Also it looks like it's impossible to have multiple adventure worlds of the same planet, possible because they do not get deleted? I'm not sure, I cannot check which world files are still on my phone.
On a side note: thank you for bringing this to Android! I won't be needing any other apps anymore.

(May be the same problem: http://forum.pixbits.com/viewtopic.php?f=40&t=30644)