Why does a Flash movie whose frames were just cut & pasted on a new frame act funny?

Why is that whenever I cut a frame, clear the frames in a timeline, paste it in new frame then test the clip, the whole thing starts to act funny?

I just don’t understand why that happens - it’s supposed to run smoothly though it’s on a new frame, right? Is there a way to maintain the movie clip when tested though some frames were cut then pasted on a new frame?