I have tried to boot older kernel versions (instead of the current 2.6.24-3):
2.6.24-2: Problem persists. 2.6.22-14 (Kernel of Gutsy): HPLIP correctly detects the printers
So as a workaround one can simply boot the Gutsy kernel on Hardy systems which were updated from Gutsy.
This also shows that the problem is most probably in the kernel. I did all my tests with a Hardy system, I only booted different kernels.
I have tried to boot older kernel versions (instead of the current 2.6.24-3):
2.6.24-2: Problem persists.
2.6.22-14 (Kernel of Gutsy): HPLIP correctly detects the printers
So as a workaround one can simply boot the Gutsy kernel on Hardy systems which were updated from Gutsy.
This also shows that the problem is most probably in the kernel. I did all my tests with a Hardy system, I only booted different kernels.