I can't make it not work. I tried it two ways:
1) ripped entire original disc to HDD, Customize+Menus, movie+3 extras, selected all subpic streams to be included. Used this to make generic.avi.xvid.audiocopy, selecting English only subpic stream, display only forced, direct render to video, auto crop, 512x???, .25 B/P. This worked perfectly, only forced subs displayed.
2) ripped chapters 2-4 of original disc to HDD, Customize/No Menus, English only subpic stream. Used the same settings in DVD to Mobile, same result, worked perfectly. All this with v6.2.2.0.
Remember that selecting more than one subpic stream in DVD to Mobile will make the direct render to video option unavailable. The first French subpic stream also has forced subs, the bottom one does not.
I have seen situations where just reading the VOBs with DVDSubEdit made display only forced not work (even with no changes to subs).