MKVToolNix seems to "auto" decimate soft-telecined DVD source?

[Treaties Of Warp]

I couldn't find any info about this using Google, etc.

I have a source NTSC DVD title that is soft telecined. The frames go P P P I I P P P I I P P P I I etc. (29.97 fps).

If I just use MKVToolNix to mux the ripped DVD title to MKV, regardless what I put for frame rate (leave blank, 29.970, 23.976), the resulting MKV file is "seen" by FFmpeg and FFmpegSource2 as only having the progressive frames. So for example if I run the "slow & accurate" frame count command (ffprobe -v error -count_frames -select_streams v:0 -show_entries stream=nb_read_frames -of default=nokey=1:noprint_wrappers=1 input.mkv), it counts only progressive frames. If I copy all frames (ffmpeg -r 1 -i "input.mkv" -r 1 frame%06d.png), only the progressive frames get extracted.

However, the exact same MKV file is "seen" by LivavVideoSource as having the interlaced frames included, just like the source DVD. (FFMpeg and FFmpegSource2 also "see" both the interlaced and progressive frames on the source .VOB files or the a mux of them to mpg.)

So, is this the correct behavior? It's as if some kind of decimating metadata is being written to the MKV file that flags the interlaced frames or something.

I'm mainly wondering how the interlaced frames are getting flagged or detected in terms of accuracy. I get a slightly different total frame count if I decimate the VOB or MPG using TIVTC. It's only off by about a second or two. So I wonder if the MKVToolNix result is better or more accurate than the TIVTC result.