Trouble printing to LPT1 using Overlapped I/O when windows is already using LPT1

When we perform overlapped I/O on the LPT1 device on a computer with a
Generic/Text only printer driver installed on LPT1, characters sent to
a non-plug-and-play printer attached to that port appear to be getting
dropped intermittently.


The problem appears to go away if we go into Device Manager and change
the "Filter Resource Method" setting on the printer port to "Use any
interrupt assigned to the port", but only until the next reboot.
After a reboot, if we switch the Filter Resource Method setting back
to "Never use an interrupt" then switch it again to "Use any interrupt
assigned to the port", we don't lose characters - again until a
reboot.


If we remove the Generic/Text only printer driver, or map it to a
different LPT port, the characters are no longer dropped.

Does any one have any ideas / suggestions?


Thanks,
Todd