Ok, this is weird:
- Following your answere, I played my own recording in JRiver: I can deactivate the subtitles now, because the subtitle stream is detected again (and thus can be deactivated).
- When I played this show live: the subs were then forced and the sub stream wasn't available for deactivation.
And now it *seems* that having deactivated them in the recorded program, it's also gone in the live streams... cannot be sure though since it can be the program that do not embed some subs, I will monitor the situation.
EDIT:
There's definitely a bug somewhere: I just browsed through the channels, live, and now I can deactivate the subs agains whenever available. BUT, when I'm turning them off, the streams disappear altogether, I cannot access them again! So it's really the same problem, but in reverse: Subs are forced off now and cannot be turned on (they do not appear as sub streams, but I know that they exist since they were available seconds ago).