What is this "spurious 8259A interrupt: IRQ15" ?

["Reuben D. Budiardja" <techlist voyager phys utk edu>]

Hello,
I've seen several of this intermittently in the /var/log/message:

spurious 8259A interrupt: IRQ15

last time this happen when I was doing rsync. I did some google search but the 
hits that I found does not really help me. I've also had some stability 
problem, the machine crash / locked up when it was rsync-ing large data from 
another server (couple days ago the server lock up 3 times in a day !). I 
don't know if it's related at all, or not. 

Here is my /proc/interrupts. At some point the ERR counting keep increasing, 
then stop. I don't really know what this all mean, but I hope someone can 
help me.

root]# cat /proc/interrupts 
           CPU0       CPU1       
  0:    2460863          0          XT-PIC  timer
  1:       1405          0          XT-PIC  keyboard
  2:          0          0          XT-PIC  cascade
  5:   14390122          0          XT-PIC  ide4, eth0
  8:          1          0          XT-PIC  rtc
 11:    2640031          0          XT-PIC  ide2, ide3, usb-ohci
 12:       4634          0          XT-PIC  PS/2 Mouse
 14:     116888          0          XT-PIC  ide0
 15:        289          0          XT-PIC  ide1
NMI:          0          0 
LOC:    2460802    2460801 
ERR:      21391
MIS:          0

In case it's useful, I have 2 IDE controllers in the system: Promise TX2 
Ultra133. 
OS: RHEL 3 with latest updates, running the latest SMP kernel.
Thanks for any help.
RDB

-- 
Reuben D. Budiardja
Department of Physics and Astronomy
The University of Tennessee, Knoxville, TN