Weird combing pattern on (progressive?) source

[Chainmax]

A friend recently bought me the Simpsons 7th season set. Seeing as they have better quality than the horrid Season 1 set I also have, I am going to try what eluded my grasp with the S1 set: make a decent rip. I'm pretty sure the source is telecined, but it displays a very weird Interlaced-Progressive pattern. Take a look at the following sample:

http://rapidshare.com/files/11429329/sample.demuxed.m2v.html

What do you think could be the cause of this?

[Guest]

2475 posts and you still don't know how to tell if a source is progressive? :)

Anime is often drawn at less than the full 24fps, then frames are duplicated to reach 24fps, followed by 3:2 pulldown to get NTSC rate.

[Chainmax]

Like I said, I am pretty sure that the source is progressive, but the weird combing pattern stumped me. The actual question was asking the cause of such an unusual progressive-interlaced pattern (the most unusual I had seen so far was P-P-P-P-I).