Well, one of my recent Kerbollo Mun missions was a partial success: I got to the Mun, separated the lander, landed and returned to orbit. And that's where it all went wrong... So the lander, while coming in to dock to the CSM, was going too fast. So it hit the main engine of the CSM, and I was like ()_() that's the first time I've ever messed up a docking! Then I said, "Well, it's not so bad: the lander has an engine. I'll just dock this thing and..." I noticed that the thing that hit the engine was the DOCKING PORT of the lander. So I've got a thing with no engine and a docking port, and a thing with no docking port with an engine... I just transferred everyone back into the CSM and launched a remote rescue vessel.