[libdvdnav-devel] DVDs w/Duplicate Subtitle Streams

[Hans Carlson]

When accessing *some* DVDs using libdvdread/libdvdnav via various software 
packages (eg mplayer, mpv, vobcopy), I've noticed the number of subtitle 
streams detected is double the number indicated in the VTS_XX_0.IFO file.

As far as I can tell the streams are exact duplicates, eg, if the IFO says 
there are 4 streams (1 each - en, fr, es, it), there will end up being 8 
streams (2 each - en, fr, es, it), in the output file.

Has anyone seen this behavior and/or know what might be causing it?

Is this how the DVDs were produced?... intentionally?  Or is it a bug in 
libdvdread/libdvdnav?  Or are the packages that use libdvdread/libdvdnav 
doing something wrong?