Kernel 2.2.16. I have added an ISA PnP modem. It is configured as /dev/ttyS1 using IRQ3. However IRQ3 does not appear in /proc/interrupts. Otherwise the device works fine.
Does it appear in /proc/interrupts while you have it open (eg while online) -if so then its not a bug but a feature. Linux knows how to reuse the IRQ for other things when not using that port.
Alan - you're right, it does appear in /proc/interrupts while the device is actually in use but not at other times. I was confused because it doesn't appear in /etc/isapnp.gone either so unless the device is actually in use it's "assignment" to IRQ3 does not appear anywhere.