Comment 32 for bug 173833

As already mentioned by Michael above you should not use the /dev/input/by-path link, you are supposed to use the
/dev/input/inputXX special file that is not a link. If you want to make sure that a specific mouse gets a specific name in /dev/input you need to create a udev rule (changing the /etc/udev/rules.d/20-names.rules file). I attach my file for an example, but you can also read more details in Michael post ant the linked page where he explains his multi-seat install.

In my file the first keyboard becomes /dev/input/mskbd0 (from multi-seat keyboard 0). Hence I use:

        Option "Device" "/dev/input/mskbd0"

in the respective keyboard section.

Repeating, don't use the by-path or the by-id link. At least for me, it doesn't work.