scanner shows up in xsane under a false device address

Question

i have a problem communicating with my Brother DCP-8040 which can be used for scannig and printing as well. I cannot really tell what the problem really is but here is the output of commands that i used to identify the problem.

firstly, since the device is connected via usb, i did

$ lsusb

among other lines, i got

Bus 001 Device 003: ID 04f9:015d Brother Industries, Ltd MFC Composite Device

the mentioned device is rw-able by the members of the group lp

$ ls -l /dev/bus/usb/001/003

crw-rw-r-- 1 root lp 189, 2 Feb 17 17:26 /dev/bus/usb/001/003

and i am a member of that group:

$groups

lorenz lp cdrom fuse lpadmin nabu scanner

asking sane about scanners gives

$ sane-find-scanner

found USB scanner (vendor=0x04f9, product=0x015d) at libusb:001:003

all the information above is not persistent. Before reboot there was always /dev/bus/usb/001/004 showing up.

all the information below is persistent.

$ scanimage -L

device `brother:bus8;dev1' is a Brother DCP-8040 USB scanner

programs like xsane or simple-scan also try to communicate with device brother:bus8;dev1

where does the false bus8;dev1 thing come from? how can i make scanimage, xsane, etc retrieve the correct device address?

kind regards