I think it is just something with the rotatron part, I have been having the same problem. I can't test it right now but maby you can put the whole rotatron and engines on the end of a decoupler droping the entire thing, it might work better and save you some weight. (not sure if this post will show up soon since my account got wiped out and they probably need to be approved for 5 posts again) *edit: nope didnt have to wait for approval, yay!