I was having the same problem and believe to have found the reason for the bug... it was only happening to me when I pushed 'r' immediately after letting go of the ladder. I have done it several times by not pushing anything and letting the kerbal ragdoll to the ground and everything was fine. Then when I pressed 'r' right after pushing 'space' to let go of ladder, it crashed again. I couldn't find a solution anywhere but from my limited testing it seems to work. Hopefully this works.