usb2: scanner no longer working

I recompiled sane-backends and linked it against libusb20. The include path
needed to be fixed.

scanimage -L doesn't detect any scanners.

sane-find-scanner correctly detects it on first run:
found USB scanner (vendor=0x04a9 [Canon], product=0x221c [CanoScan], 
chip=GL842) at libusb:/dev/usb:/dev/ugen3.2

on subsequent runs no scanners are found

dmesg only says
ugen3.2: <Canon> at usbus3

no ugen detached message even if I unplug the scanner

I tried some of the debugging sysctls but I couldn't spot anything useful.

ugen seems to work in general as I could access my camera with libgphoto2.

Will provide more info as needed.

-- 
Stefan