text: try a different editor?  i don't recall having that problem with potlatch, and josm should give you enough rope to shoot yerself in the foot in ways that others will struggle to clean up with their editors.
  
  dunno about the split issue, as i've never had problems correctly splitting things in a relation and preserving everything across all parts.  then again, it sounds like a protection against shooting yourself in the foot.  you are speaking of iD editor, no?
  
  i'd try to edit here in potlatch but i'm not awake enough to understand what you need done, sorry