My experience says that Filemaker's relationship with printer drivers is nefarious at best. I'll guess that somewhere, sometime, somebody, possibly a designer, modifying a print, or print set-up (and maybe a script step), printed two copies, and for ever, plus one day, FM will remember that.
If it is possible, try opening the database on one of the defaulting workstations - that is: opening as the host. No guests. Print correctly. If it is part of a script, re-define the print section of the script to be correct. Then close the file. Now open it again and host as normal.
If your database is hosted over a network, try bringing a copy off the server onto your local machine. Reset the printer settings and then put it back up. That sometimes clears out such "gremlins".
You can also experiment with this advanced recover option: "Delete Cached Settings, (Page Set up, sort order etc.)
and see if that recovered copy exhibits the same default settings.