Thanks for this. It’s early here too….
I’ve been playing with this over the last hour, and I’d started to come to the same conclusions.
The combing problem definitely occurs on both preview AND the rendered output. In fact, it was only the client looking at a sample of the render on his own DVD player that spotted the problem, I’d had preview set to a lower quality and hadn’t seen the problem in any of my usual checks.
Just running some tests and the only way I can lose the problem (in auto quality preview at least) is to set the field priority to Progressive. So maybe it’s a similar problem to the one you had. I’ll keep playing…..