Why does combing commonly occur on scene changes?

[dbzgundam]

I noticed on quite a few DVDs, even those that are supposed to be progressive, that there *are* combs, very few... I'm not really concerned about them, as their extremely small number makes them easy to get rid of.

I'm just curious; why do these randomly combed frames typically happen on scene changes (and I notice it frequently happening on chapter stops actually...)?

[neuron2]

They happen at scene changes because the authors are not careful. They put cuts between fields instead of at frame boundaries:

Bad cut:

A B | . D
A . | C D

Good cut:

A B | C
A B | C

Even if the clip is interlaced, such that all frames are combed, you'll notice combing at the scene change much more because the two fields are very different because they come from different scenes.