From the makemkv FAQ: (http://www.makemkv.com/faq/item/10) "Unlike DVD, on Blu-ray, each subtitle item has an attribute that specified whether particular subtitle appearance should be forced."
But actually,DVDs also have subtitle attributes that specify whether individual subtitles should be forced.
Is there support for these types of subtitles?
For reference, I have found that BDSup2Sub can scan an extracted VOBSUB file for these forced subtitles, and even extract only the forced subtitles, which can then be merged back into a mkv file. The result I assume is similar to makemkv's forced only option for blue-ray discs. (I dont own any blue-ray to test though, only dvd)