[Tyhm]

Another way to get that sort of error:

Open a level (like bob.graal).
Close the level.
Open another level (steve.graal).
Save this level with the original level's name (save steve.graal as bob.graal)
Close the level.
Open the original level (bob.graal)
Say "OH NO, WHAT HAPPENED TO ALL MY CHANGES!" - it will be the original bob.graal
Close Graal.
Reopen Graal.
Open bob.graal. It will be the copy of steve.graal like it's supposed to be.

What's even more distressing, you'll get the cached level even if you don't close it - you load a level, change it, tab over, tab back, changes gone, that makes me a sad panda.