I think you may find that this does happen and if you get residual stuff left behind like a door after deleting a prefab or segment then you may have to select again the individual objects from the segment or door libraries and use the arrow pointer to right click and remove the objects one by one. Sometimes numerous attempts at placing and deleting the offending room segment may get rid of it all.
A nusiance I know but dont think theres another way around it.
I dont think its anything you can do anything about - its just the way FPSC is.
