Maybe I should have offered a bit more information.
I researched a bit and found out subtitles from HD discs are in a unique format and apparently troublesome. Much as I dread codec packs I installed the Shark packs and followed the instructions which resulted in the LAV decoders and DirectVobSub being active in MKV playback.
The subtitles are shown as active in the DirectVobSub taskbar applet but they are not displayed. In the case of multiple subtitle tracks in the mkv, they are all shown as selectable, so they are evidently identified by DirectVobSub.
Then I tried using MKVcleaver to extract the subtitles to .sub files and put them in the same folder as the mkv file. That did not work either. So I googled some more and found out about BDSup2Sub which is supposed to be able to convert HD DVD subtitles to a standard format.
But BDSub2Sup chokes ("Invalid Control Buffer Size") when I try to feed it one of the subtitle files extracted from a MakeMKV-created MKV file.
However, if I extract the subs directly from the EVO files on the disc/ISO, BDSup2Sub reads them.
So the conclusion is MakeMKV does something to the HD DVD subtitles that renders them unreadable, both directly from inside the MKV and if extracted.Edited by politby - 4/30/13 at 12:37am