The linux 2.4.18 distribution kernel contains a small but critical bug handling parallel port interrupts. The bug only affects the parport_pc module so only IBM PC style parallel ports should require this patch.
The bug has been corrected in 2.4.19-pre2, and did not exist in kernel distributions prior to 2.4.18. The patch provided below functions on vanilla 2.4.18 kernel distributions, but has not been tested extensively. It should work, but no guarantees are expressed or implied.