This bug also exists in the 13w03a snapshot, except it appears you are only allowed to have 17 maps saved at a time before it erases the primary maps you started with in sequential order.
This was only a problem in the 1.4.3 update. The issue appears to have been fixed since and is no longer an issue.
This bug also exists in the 13w03a snapshot, except it appears you are only allowed to have 17 maps saved at a time before it erases the primary maps you started with in sequential order.