This isn't the same bug I reported last time.
I don't know what exactly I did to cause this, but somehow the editor set ALL event trigger options of every single block and NPC in the entire level to trigger an event when I created it, unless they were set to anything but [none]. So activate, death, hit, and "no more objects" event triggers of NPCs and blocks were all set to this event, and I had to go through the whole level to fix it. It's a good thing I could select every object in the level at once. (Just about crashed the editor, though)
I tried, but I was unable to reproduce this bug. This probably isn't of much help to you, but maybe you can figure out what the problem is.