I had this glitch a while ago with my old game. A lot of my actors were deleted, but I had over a hundred new behaviors. I deleted the game because I hadn't heard of this before and I was afraid it was a virus, but a lot of those behaviors were new, not replicas of old ones. It kind of creeped me out, because I couldn't find the behaviors on Stencylforge and they worked perfectly.
I got the same bug with my newest game, Monster Age(Check my topic) but I can open my game and use it fine. I also cannot publish my game to the website, but I'm not sure whether that's related or not, since this bug has been going on for a long time before this started happening.