cannot change subtitles or language via rc

[npem]

Hi,
I am playing a DVD via:
/Applications/VLC.app/Contents/MacOS/VLC --extraintf rc --rc-host localhost:1234
(version is 1.1.10.1)

If I then telnet to port 1234, I cannot change the subtitles or language both of which are available to select via the user interface)

I have tried, for example:
vtrack 1 (and other numbers)
strack 1
atrack 1

but no changes take place in the subtitles or spoken language.
Anyone know why (and what command I should use)?

Thanks in advance
Phil.