Aopen burner burns image files but not DVD files

Have an odd (to me anyway) problem with an Aopen Chameleon DVD burner.
This is actually a replacement I got from Aopen when the first one I
got from Cheapguys didn't burn at all.

When I try burning DVD files - i.e. the video.ts files, the resulting
disc is full of crackles. It burns Nero .nrg image files made from my
Cyberdrive DVD burner fine however. I updated the firmware at the
suggestion of Aopen tech support, made no difference.

I imagine I'll be sending this one back too, but I'm still curious.

Anyone have a guess as to why this might be?