Known issues with using digital camcorder as pass thru for analog VHS tape?

In the past I have been able to use my Sony DV33 as a pass thru to convert old VHS tapes to digital in iMovie. I recently bought a cheap VHS/DVD combination player unit for the kids (Samsung - old one died) and for some reason iMovie will capture anywhere from 1 to 4 seconds and then stop capturing.

Has this ever happened to anyone else?

Thanks.