While I was watching a movie on a DVB-T channel, I recorded this movie at the same time on my external USB HDD.
The subtitles could not be shown on the TV screen, but when I stopped the recording they appeared again.

When I afterwards played this partly recorded movie the subtitles were present on the recording!

It seems like the subtitles are removed from the TV screen while you make a recording at the same time.

My TV is a 40PFL8007T (newest software from a week ago)