This happens to me anytime I change the number of copies in the Print window....it stays until I make a change again then print an entire return again.

So open some simple return, open the Print Return window and change to 1 then print out the entire return, this will reset the copies back to 1 the next time you print.  It wont hold the change if you only choose to print 1 page, another weird quirk of proseries.