multiple spontaneous garbage jobs

[Jim McCloskey]

Hello.  I recently set up a new printer (a Dell 2330dn) in a graduate student lab that I'm responsible for. The lab has 4 OSX machines and 3 Debian Linux machines, all running various versions of CUPS. The OSX systems run CUPS version 1.1.23. Of the Debian systems, one runs CUPS 1.2.7 and two  run CUPS 1.3.8 (as packaged for Debian).  I installed the PPD file that came on the CD with the printer from Dell.

The OSX systems are problem free.

The problem is with the Linux boxes. They seem to be spontaneously sending to the printer every few seconds jobs which result in the printing of what looks like a header page.  The pages printed look like this:

POST / HTTP/1.1
Content-Length: 263
Content-Type: application/ipp
Host: xxx.xxx.xxx.xx
User-Agent: CUPS/1.3.8
Expect: 100-Continue

followed by a single line of characters which are mostly unreadable and which spill off the end of the physical line in a manner reminiscent of the stair-case effect (some of the characters are over-printed and illegible).
The three machines have so far printed thousands of such pages and used up quantities of toner. Yet no user has sent these jobs to the printer. The only way to stop the flow of these awful single-page jobs and the incredible waste that they entail seems to be to kill the CUPS daemon (then they stop) or else to de-install CUPS completely (they also stop then). But the jobs resume as soon as CUPS is restarted or reinstalled.

Printing to the printer otherwise works fine (i.e. when actual users send jobs) but obviously I've had to disable printing entirely on the three Linux systems.

I've set up CUPS on many Debian boxes and never had a problem so frustrating before (never had a real problem before in fact); but this is just maddening.

Is there anyone here who could give me a clue about why this might be happening?
What or who is sending these jobs to the printer and how do I stop it?

Thanks very much in advance for any help you could give.

Jim