this post only to explain why in some case fast forward and rewind doesn't work in MKV.
The problem is related to the version of mkvtoolnix (and related mkvmerge) used to create the mkv.
Basically if you create the mkv with a version 4.0 or >, the Samsung BD reader (and may be also the television) doesn't handle the mkv in the right way. If you use a previous version (e.g i used the 3.4) everything work fine.
This is not a problem related to serviio but to the samsung firmware/codec. In fact the same problem exist also when you copy the mkv to a usb drive and you try to run it direcly from the player.
So the way to fix the mkv than doesn't fast forward or rewind is:
1) Install mkvtoolnix 3.4
2) Open the mkv with this version and resave it