Comment # 7 on bug 911312 from Johannes Meixner

According to the output of
  rpm -qa --last | grep '^cups'
in comment#3
cups-filters-ghostscript and cups-filters were installed after cups
so that there is the /usr/share/cups/mime/cupsfilters.convs file
which is required for normal filtering.

>From your attachment#618838 [details] "Initial y2 install log"
I cannot determine the ordering how the cups* RPMs have been
initially installed.

I guess initially cups-filters-ghostscript and cups-filters
had been installed before cups so that there was no
/usr/share/cups/mime/cupsfilters.convs file and you got
the non-working filtering via pstotiff.
This would match
https://bugzilla.opensuse.org/show_bug.cgi?id=906198#c4

Therefore I think I need to improve the RPM %pre scriptlet
in cups-filters-ghostscript to make it work independent
of the ordering how all those cups* RPMs get installed.