I finally found what was the issue. I was still running kernel 2.6.28-6-386. Now I'm using 2.6.28-15-generic and everything is fine.
So the upgrade process from 8.04 to 9.04 somehow failed to install the latest kernel, which broke the wacom support.
Could that be because I once manually edited /boot/etc/menu.lst? The changes I once made were under the line '### END DEBIAN AUTOMAGIC KERNELS LIST', while the outdated kernel I was using was mentioned above that line.
I finally found what was the issue. I was still running kernel 2.6.28-6-386. Now I'm using 2.6.28-15-generic and everything is fine.
So the upgrade process from 8.04 to 9.04 somehow failed to install the latest kernel, which broke the wacom support.
Could that be because I once manually edited /boot/etc/menu.lst? The changes I once made were under the line '### END DEBIAN AUTOMAGIC KERNELS LIST', while the outdated kernel I was using was mentioned above that line.