HSync issue on Composite capture - PVR500

[PDO]

I've got a new Hauppauge PVR500 card in a newly-installed Debian "Etch" (4.0 r0, kernel 2.6.18) system; ivtv drivers.

The card seems to be working fine, as demonstrated when I hook up a VCR to the (composite) input(s).

And I've got a new Sony SSC-DC374 surveillance camera (NTSC video output, BNC -> F adaptor; RG6 coax cable; F -> RCA adaptor), which seems to be working fine, as evidenced when I hook it up directly to a TV, or record its output on my VCR. Clear, sharp, stable images.

BUT: if I hook up the camera directly to the composite input(s) on the PVR500, the image scrolls horizontally at a rapid rate (viewed via mplayer, captured via ffmpeg, etc all give the same lousy result). Occasionally, it might produce a stable image, but seemingly never for more than a few seconds.

I get the same horizontal sync problem when viewing the image while hooked up _through_ the VCR. But if I (simultaneously) record the image, the image playback from the VCR is fine and stable (even though the "live" image wasn't).

Any ideas? Is the card known to be sensitive to HSync issues?

[PDO]

New information: connecting the camera directly to a PVR150 (which is about 2 years old), it's showing a beautifully stable image.

Is there any known sensitivity issues on the PVR500? Any configuration settings I might check?

[PDO]

New information: by reducing the screen resolution (thus, presumably, the amount of work the machine has to do on each screen refresh cycle), the image seems to stabilize. (Note: even adding a video card to offload processing from the mainboard didn't help).

But I still don't understand this: why would a simple frame capture (e.g. ffmpeg, or cat /dev/video0 > file.mpg) be so unstable? Is there anything I can do to ensure better stability?