Whoops! I spoke too soon. :doh:
While the first two films I did showed the subtitles in the preview when they were forced, the next two did not.
It's really a problem, as a lot of new films have regular English subtitles and also English SDH, plus some also have the director's commentary as well. If I force the wrong one, my archive doesn't play the one I want. Seeing them in the preview thumbnail would solve this.
Hope Fengtao has got this on his to-do list.