PGS subtitles will not display

XBMC 12.2 on Fedora 18

Any video (Matroska container) I have with PGS subtitles do not display when played by XBMC. The xbmc.log shows the subtitle tracks being opened, but nothing else to indicate a problem. The audio/subtitle menu shows the subtitle tracks (Japanese/English/etc) but they never show up on the screen.

Other subtitle types display inside XBMC just fine. I can play the PGS videos and see the subtitles with mplayer or Totem.

Any ideas?