That sample is strange. I've only looked into it for a minute, but ffmpeg isn't happy with it either. Running "ffmpeg -i kuchikirukia\ -\ won\'t\ mux.ts -an -c:v copy ffmpeg.h264" produces an empty file; the similar "ffmpeg -i kuchikirukia\ -\ won\'t\ mux.ts -an -c:v copy ffmpeg.mkv" produces a Matroska file with track headers & tags but without any frame.
As to mkvmerge: the option is called ""--engage all_i_slices_are_key_frames" (additional "_" after "key"), BTW. You can mux the file that way. There are I slices every 500ms which will all be marked as key frames.
If I use mkvmerge with "all_i_slices…", extract the h.264 from that and import into an MP4 with MP4Box, then none of the frames are marked as key frames in the MP4 file (the "stss" atom contains an empty table).
If anyone else wants to take a look: I'll leave the file up
here for a while.