After setting up an avision scanner with yast successfully, every time, the
user is executing xsane, the system queries for root permission for a polkit
action: org.freedesktop.systemd1.manage-units. Why? 

User can dismiss query, and xsane is working fine.


Specific setup:

$ sane-find-scanner 

  # sane-find-scanner will now attempt to detect your scanner. If the
  # result is different from what you expected, first make sure your
  # scanner is powered up and properly connected to your computer.

  # No SCSI scanners found. If you expected something different, make sure that
  # you have loaded a kernel SCSI driver for your SCSI adapter.

found USB scanner (vendor=0x0638, product=0x0a5e) at libusb:001:004
  # Your USB scanner was (probably) detected. It may or may not be supported by
  # SANE. Try scanimage -L and read the backend's manpage.

  # Not checking for parallel port scanners.

  # Most Scanners connected to the parallel port or other proprietary ports
  # can't be detected by this program.


udev sets up this device just fine:
$ getfacl /dev/bus/usb/001/004
getfacl: Removing leading '/' from absolute path names
# file: dev/bus/usb/001/004
# owner: root
# group: root
user::rw-
user:username:rw-
group::rw-
group:lirc:rw-
mask::rw-
other::rw-

How scanning is related to lirc escapes me. According to
/usr/lib/udev/rules.d/55-libsane.rules, the group is "lp" for such devices.
Therefor, I added the additional lp group to username. 

The whole issue boils down to: why is polkit querying for root permissions?