Thanks for the report and the log file.
For every option combination, the log file writes "Options support paper
size 'xx'". The other possibility is never written to the log file.
I suspect the culprit is the fact that the fujitsu backend is returning
SANE_INFO_INEXACT for many of the geometry options and gscan2pdf is
getting confused between them.
I'll work on reproducing the problem with the test backend and then on a
fix.
I appreciate that the bug is important for you, but I think it is
specific to your backend, and thus only affects those gscan2pdf users
with fujitsu scanners.
