So I have gotten this Xerox Phaser 6125 printer, and I have installed
the driver you mentioned, but a single problem stills bug me.

When I try to print multiple copies, it print the squared number of copies.

So if I try to print 2 copies it prints 4 and if I try 3 it prints 9 and so on.

I have the problem both in Gnome Print and in lpr.

I suspect that the copy operation occurs 2 places and that results in
a squared number of copies.

Does anyone have a suggestion on how to fix it?

IIRC I had the same problem on one installation, sadly I never troubleshooted it and that system is gone so all I can do is verify that the problem may appear but no idea of why. All later setups I've done has worked.

On Fedora (20) currently, the problem of multiple copies has also bothered me. The number of selected copies comes out squared, so if you select 2 copies, you get 4, select 3 and get 9 etc.

I fixed it by putting an extra filter in between the cups and the Fujitsu filter chain.

create a file /usr/lib/cups/filter/fxm_pf:

Make sure this file is owned by root, and set the proper permissions for this file:

chmod 755 /usr/lib/cups/filter/fxm_pf

Edit the ppd file (normally in /etc/cups/ppd), and change the line with cupsFilter to:

I.e. instead of the original Fujitsu filter, FXM_PF, call our modified filter. The modified filter changes the number of copies to 1 and then calls the original FXM_PF filter. Apparently cups already generates collated copies, and forcing the Fujitsu filter with 1 prevents that one from multiplying that again.

Happy printing