I did a search for 'wsave' and 'auto context saving' in the 16F1847 data sheet but nothing found
hi bill
basically any chip that has auto context saving requires no additional code/vars to save the context, for the priority interrupt anyway.
wsave psave fsave... are a legacy of old chips .

As to the version of PBP3 I'm using... is it freely available or is it a purchased upgrade?
its free upgrade for licenced pbp3 users, you are quite a few versions behind ditto for mpasm . it may be the issue.
but it won't hurt to upgrade