I updated my Apple TV today, it's a great upgrade for Media Player!
However, playing my usual TV Shows and Movies in 480p and 720p MKV with SRT external subtitles, I noticed a glitch, a certain type of jumps in the video when a subtitle appears on screen; causing little jumpings all over the video when a subtitle pops up. Very annoying.
I tried to fix it by changing the color, size, and outline of the subtitles and nothing... even with MKVs with a lower bitrate.
I hope you can fix it as soon as possible on the next update.