[Endoperez]

The battle movies aren't recorded; instead, the battle is recalculated from the same random numbers every time you view it. If for any reason the random numbers don't match or the battle is replayed differently, the movie will play differently. What happens to your units is based on what happened when the host went through the battle, of course.

One instance of this bug only appeared with spesific spells and different operating systems, playing with mismatched versions of the game can cause this, etc etc. It can be hard to catch the reason with just the turn files from AFTER it has happened; if you happen to have the previous turn (.trn or even fthrlnd and .2h) somewhere, I suggest posting that as well. And yes, you should report it in the bug thread, but while the general cause is known it's hard to know what, exactly, causes this bug in any spesific case.