I found a couple more bugs:
1. Mouseover has a barrier in the y-axis that it can't go below. If you try to mouse over a door or key that's too far downwards, the info box will appear significantly further up than it should. This applies both in the editor and in gameplay. (I'm not sure whether there's also an x-axis barrier)
2. The description of the levelpack and the author/s of individual levels are not saved. The rest of the level info (levelpack name, author/s of the levelpack, names and titles of individual levels, etc.) is saved, but not those two bits for some reason.