I have many mkv movies that played fine until I updated the firmware to 3.00.28. Now the subtitles are no longer displayed even though the subtitle language is selected. My mkv files all have the subtitles encoded within the file itself (not seperate sub files). I have 2 Live Hub units and both have the same issue. One other issue I am having is one of my units looses content of its internal storage quite regularly. I have to clear the media library and have it re-scan to be able to access the content again. Both of these issues were not present until the firmware update.
Yes, there are reports of this issue with the MKV movies. The only fix for now is rollback the firmware.