Touchpad device changing from event1 to event0

[Michelasso <qzerty@gmail.com>]

I have notice today that the touchpad of my Acer Aspire 5024 wasn't
recognized  anymore by the x server as a synaptics one, even if the
kernel says (according to dmesg) that it is a synaptics one. After
investigating for a while I have noticed that the device associated to
it has changed from /dev/input/event1 to /dev/input/event0 according
to /proc/bus/input/devices. Since in my xorg.con I have the line

Option          "Device"                "/dev/input/event1" 

of course the server couldn't recognize it. My question is: why has it changed?
(I am sure that before it was event1, I had checked it in
/proc/bus/input/devices and it worked)
Could it be due to the installation of a new kernel?