I think I may have discovered away to make a polyobject cross a linedef.
Okay, say you had a polyobject, and you wanted it to cross a linedef, it would cause a SIGSEV because it would still be it's own sector, but the vertices would have stitched to the lindef, causing it to be on the other side of the linedef you just had it cross, but it would still have the properties of the previous sector, blah blah blah. The point is, it SIGSEVs, so why not make a polyobject that was split into two, with the dividing line parallel to the one being crossed, the two polyobject sectors would originally share properties, until the verticies would (normally) stitch and would split the linedef and cause a SIGSEV. Instead, it should stitch with the dividing linedef and change the properties of the portion of the polyobject on the crossed side of the linedef to match what's below it. once the dividing linedef reaches the edge of the polyobject, it should turn the uncrossed side into a nonexistant sector with some zero length linedefs.