How to reproduce: use any girder, attach a hinge to it. Use either "move" buttons in group editor (<-/->) or position editor gui. Open the hinge a little, close it, repeat until it starts to collapse into itself. See screenshot:
Note the "-1" in position editor. Problem appears to exist only in editor, I wasn't able to reproduce it in flight.
How to reproduce: use any girder, attach a hinge to it. Use either "move" buttons in group editor (<-/->) or position editor gui. Open the hinge a little, close it, repeat until it starts to collapse into itself. See screenshot:
Note the "-1" in position editor. Problem appears to exist only in editor, I wasn't able to reproduce it in flight.