Capt Jock,
Yes I wondered about that myself, though both parishes seem to have been in existence at that time (1790). Perhaps the parish boundary was changed at some time. Another possible explanation, and one I have come across several times myself, is that Donaghcloney parish church was temporarily closed eg repairs, and so the nearest adjacent parish church was used instead.
With Banoge being right on the border with Magheralin, as Shane helpfully pointed out, I am pretty certain I have the answer to my puzzle.
Elwyn