PAL DVD interlace problem

[signal]

Could someone be kind enough to confirm what I'm seeing here?

This particular PAL DVD starts out as a typical 24fps film sped up to 25fps and progressive frames split over two fields.
Awesome.. no interlacing/telecine to mess with.

Or so I thought. About 16 minutes in it looks like a single field is getting dropped causing successive frames to be non progressive.

The rest of the vobs show the same problem until 1hr and 6 minutes later when it is correct again (total film length is 1hr 36min).

This doesn't happen at any vob/chapter transition.

DGIndex doesn't show any anomalies and watching the original dvd from disc in VLC confirms the same thing.

I started looking at using SeperateFields(), drop the problem frame/field, combine fields again but not having much luck yet.
Thought some other eyes on this to confirm what's happening would be more helpful at this point.

Here is a sample 2min vob made with vobsplit (without any re-encoding), my d2v, and avs to show frame number.
The issue starts at frame 1213.

Sample.7z (80MB)