Could not check myself anymore as I deleted both after watching. No idea what is causing the problem then.
I was going to try dvdfab to see if it is indeed cinavia (and remove). but it requires the 64bit ver for 4k contents and my pc is just 32 bit. if someone can try and confirm, that would be great.
Looks like MKV playback isn't the only thing to suffer... In the transition from HT2 v2.5.* to 2.6.* it seems that collections have attracted a few issues too... http://forum.zidoo.tv/index.php?threads/movie-wall-help-needed-please.50434/page-2 Come on guys, you're breaking more than you're fixing at the moment - we're not used to this!
Green screen is back. when i pressed 'ok' to pause on a 1080p mkv (z9s video setting set to 4k), a green screen flashed after 10-20 sec. playback is fine. not a major problem, more an annoyance.