Subtitles problems with F8500 BluRay player

While trying to watch game of thrones with Greek subtitles, I realized that they are not recognized using Serviio on both of my F8500 and the file plays as if there were no subtitles, with no subtitles option in the tools menu. If I try watching it with English subtitles, they show up, but all the subtitles options from the tools menu are greyed out (sync, size, encoding etc) and not selectable. If I select "Enable burned-in subtitles" from the Serviio console menu, I can see the greek subtitles but then I cannot use fast forward, rewind or resume on file and no subtitles options appear in the tools menu. Playing the same file through the USB port of the player wields flawless subtitles function. Playing the same file on the same LAN on an older C8200 Samsung BluRay player wields flawless subtitles function. Using Samsung's proprietary media server (Allshare), again, wields flawless subtitles function. So the problem is with Serviio. Will be sticking to Samsung's memory hog until (and if) this is fixed...

By the way, this occurs with all my video files (a very large library), not just the game of thrones file