I tried it on two different players, both with the same outcome. The sound does not skip though.
It’s only a minor glitch and I should not complain, but as a Fan… 😉
I just checked, there is no such encoding error in the “official” mkv v2.7. So this issue must come from your friend’s encoding.
Or the player might be converting 720p24 to 1080i for HDMI transmission, and the TV’s turning is back into 1080p and one or both of the devices are not handling it well. 720p24 does invite player problems because it can’t be transmitted over HDMI natively.