Kerbal Space Program

A number of versions back I once built a rover on a boat suspended under an aircraft, as part of a challenge I did with a few friends. Now I wanted to retry this, and I built another rover on a boat. Now it appears that rover wheels don't recognise a collision with another part as opposed to the terrain, as the wheels fall through the underlying parts and the rover cannot drive onto the boat again, if it ever comes off in the first place. I tried it with the medium rover wheels with inflated tyres, a friend tried it as well with the other medium wheel type. Attached are the craft I used when I encountered the bug.