Version compatibility of files

A lot of people use beta. A lot of people also have their startup settings set to "open previous session". A lot of people need to get work done, so they temporarily convert back to the stable release so they don't have to deal with bugs...

0.9.5 starts up.... automatically attempts to open previously worked-on file, and due to backwards incompatibility, is unable to open it. But that's not all - for some reason, it decides it has to corrupt the file as well, so that when you try to go back and open it up in the beta, that's also broken now. In a flash, all your work is destroyed with no chance of recovery.

Question: why does the mere act of attempting to open a version-incompatible file corrupt the file, as opposed to simply throwing up a "this version of MuseScore can't open this file" error?