Official Everybody Edits Forums

Correct me if I'm missing something, but I just realized the levels files extensions saves as a different file extension instead of the usual file type every time you save a world for some reason.
Once a world has been saved, you cannot open the level again, because the game can only open any level/world with the default file type, and if a level's file type does not match the default extension, it will not appear on the "Open Level" list.

Not sure if it's a "me" issue, or it's been this way ever since, but overall, the update is fabulous.