I don't dare to think how many of those invisible saves are littering my device after having built and playtested half a dozen maps, making constant changes and starting again and again...
The easiest way to fix this would be to delete any attached saves when you delete a self-made map from the "Own Maps" list. The most safe would be to ask each time the player quits if the game should be saved or not. The most elegant would be to include some savegame management feature (allowing you to delete irrelevant saves).