I'm not sure if anyone else's copies are affected, but I'll say it on here just in case.
On my copy of Puella Magi Madoka Magica: Rebellion, you can't switch off the subtitles on the special features. Luckily, you can still switch off the subtitles on the main feature though.
The reason for stating it here is because when people try to switch off subtitles on a feature that has locked subtitles, it would normally come up with "this action is prohibited on this disc", from what I read in various forums as I don't own a copy of any show or film that intentionally has locked subtitles. However, when I tried switching them off on the special features, for some reason, when I press the subtitle button, it still comes with "On/Off" on the screen, meaning that the special features probably weren't meant to have locked subtitles during playback. By the way, they're not hardsubs, as when I rewind or fast forward the special features, the subtitles are not present, meaning that they're still softsubs. And if I'm correct, they're taken from Aniplex of America discs, which (once again) if I'm correct, they don't have locked subtitles on their discs due to their high prices (another way to prevent reverse importation).
Strangely, I never had this problem with the special features on my copies of the first 2 films, Beginning and Eternal.
EDIT: I forgot to add that this is for the Blu-ray release.