Recently there's a new firmware 1180.3 for the H6600 series.
Since this new firmware there's a big problem with playing MKV files that have embedded subtitles. The video freezes after a few seconds and then the TV reboots itself. If the MKV does not have embedded subtitles, it plays fine.
It seems to me that Samsung have messed something up. Most MKV files you can find, for example movies, have embedded subtitles, so many people will probably have these crashes / reboots.
If you already have Firmware 1180.3 installed and have this problem, please report it to Samsung via their support form. This way they can realize that they have messed up with the firmware and hopefully fix it.
Warning about H6600 Firmware 1180.3 - freeze/reboot
Re: Warning about H6600 Firmware 1180.3 - freeze/reboot
New firmware 1200.2 from yesterday finally fixes this. Merry Christmas.