VLC does not display vobsub subtitle tracks beyond the first

When I export subtitle from a dvd using mencoder as such: mencoder dvd://1 -nosound -ovc frameno -o /dev/null -slang en -vobsubout Output

If the movie has multiple subtitles I want to keep, I re-run this with different language or -sid (instead of -slang) options. Mencoder will concatenate each pass into the same Output idx/sub pair, so the file winds up with multiple subtitle tracks. I'll paste an example of the idx file below, where both tracks are english, the first track is visual translations only (e.g. signs shown in the video), and the second track has the full dialog.

When VLC opens the Output.mp4 video file, it finds the sub/idx pair and does show two subtitle tracks available in the subtitle menu, but when I select the second one I don't get any subtitles at all. When I choose the first one, I get subtitles from the second track.

I see this on OS X, VLC 2.1.5 Rincewind (Intel 64bit)

size: 720x480 palette: d7410d, 210f26, d5d5d5, e7ff26, 0f140e, 101010, e7ff26, e6ff28, d717cc, d6a80b, 8b02d6, 0ab780, 373737, 95679f, 8caa67, 783d3f

ON: displays only forced subtitles, OFF: shows everything

forced subs: OFF

Language index in use

langidx: 0

id: en, index: 0 timestamp: 00:02:09:596, filepos: 000000000 timestamp: 00:09:14:145, filepos: 000001000 [...]

id: en, index: 0 timestamp: 00:00:21:246, filepos: 000040800 timestamp: 00:00:23:073, filepos: 000041800 timestamp: 00:00:27:911, filepos: 000043000 [...]