nixCraft

Hi, I need some help!
I am using an HP Deskjet 5150 printer with USB interface. The printer connects to port ugen0.2. After boot, as "root", I load manually the usb printer driver ulpt0 (kldload ulpt0).
Now, if I simply copy a deskjet-formatted print file to ulpt0, the printer prints correctly. (cp xxx /dev/ulpt0)
If I try and print via the LPRng spooler (with etc/printcap properly set to ulpt0), nothing happens. Nor do I get any error message.
If I run "checkpc" I get the message that access to ulpt0 is denied.
When I set ulpt0 to rw,rw,rw with "chmod 666 ulpt0" and try and print again, the printer works fine.
So far so good.

The problem is that after a while, when the printer goes in standby, ulpt0 is reset back to "600", i.e rw,r,r.
Strangely, if I again simply copy a file to ulpt0, the printer prints fine, but the spooler does not work - at least till I reset manually ulpt0 to "666".

Why is "666" required? what is resetting it back to "600". I am really lost.
I hope someone can give me a hint.
Thanks.
Regards, GR