Are you both working on large project?
Another way to look at the problem is the undo list. Im working on a rather large project (lots of images, events, layers, etc), and the strangest version of this happened yesterday.
After a couple of hours working without a crash, I held the alt key for a few seconds, and then it crashed. Just in the editor, looking at an event sheet. It may have been saving at the time, but that was it.
I wasn't alt-tabbing or anything (I was going to but got lost in thought, hence the holding down the alt key).
I'm certainly not qualified to figure this out, but maybe it's a memory problem that's triggered after a certain point, which is reached faster by projects with more assets?