Sony - why the same MKV would show up as "MKV" and "MP4"?

[tmeader]

I recently upgraded from a BDP-S590 to a BDP-S5100 (but this model turns out to have MAJOR issues streaming via UMS, almost nothing streams, despite being identified as a "Sony Blu-ray" and having, on paper, the same supported formats, plus more, of the 590). The latter is going back due to all the issues unfortunately, but I'm still seeing some strange occurrences that are quite annoying (using 2.6.5 on Windows 7 x64). I've got the Blu-ray of Iron Man 3, so I obtained a nice MKV copy to play via UMS on my player at times when I don't have the disc in. I realize the legality is debatable, but I was going to rip it anyway, so this was simpler. Anyhow, this copy has multiple subtitles (roughly 18) as well as two language tracks. All the various subs aren't required, so I remuxed it via mkvmerge 6.4.1, simply removing the subs I didn't require. NOTHING else was changed. Anyhow, the issue is that, if the player recognizes the file as "MKV", then it will support the subtitles enbedded in the MKV, and you can easily enable them as you play it. Likewise with the alternate audio tracks. When it recognizes the same files as "MP4" however, it will still play fine, but you are unable on the player to enable the subtitles or switch to the alternate audio tracks.

My question is why one would be identified as "MKV" while the exact same file (simply minus 16 of the embedded subtitles) is identified as "MP4"? Running the graphical version of MediaInfo on both files shows them as identical except for the versions of mkvmerge used to create the two (the original was created with 5.8.0). Would this make that large a difference?? I've enabled all the options cited in the mkvtoolnix FAQ section for player compatibility, so I wouldn't think that would be the issue.

Any help would be greatly appreciated, as I'm at a loss as to why the exact same file is being seen differently just by removing useless subtitles. Thanks in advance.

[sukh77]

Seems like the program (mkvmerge 6.4.1) changed the format to .mp4 when you remuxed it. See if there is an format output setting somewhere in the program.