Not sure if it has anything to do with the bug above, but I also ran into another weird bug (but don't remember how to reproduce).
I was working on a behavior, and after some time it gave me an error whenever I tried clicking on any events (on the left side of the behavior). Basically it disabled me from switching to any other events in that behavior besides the one I was currently on. I had to close Stencyl and restart to resolve this issue.