Insulation over ceiling drywall nailers or scabs
no.no.no.  don't slit the paper.  its there as a vapour barrier.  having your insulation humped up over the backing is no issue, as long as your vapour barrier and insulation are complete and with full integrity.  just make sure that there are no gaps between the adjacent insulation and your humped piece of insulation (ie. where cold air can get down against the cold side of the drywall.  here in Ontario, nobody has used paper backed insulation for years.  we have the requirement of a seamless plastic barrier, taped, pocketed and sealed at all penetrations to make a giant air balloon out of every heated space.  the logic is the same for any place on earth, even if you are working with old materials or new materials that use old technologies.