text: I doubt the deliberate overlaps are frequent though I'd expect accidental ones to actually be common.  I think the easiest accidental way to cause them is to put too many points close together and someone clicking and blindly dragging the wrong point, and it still looks good even when it's not...
  
  Then the other thing I don't know is how well conflict resolution works when more than one edit works on one spot if the same nodes are extant (i.e. no deleted nodes)... this is maybe what you're talking about?
  
  Still lots to learn.