[mythtv-users] Changing channels gets no sound until I switch audio tracks

[ffrr]

When I change to a new channel, sometimes there is no sound until I use 
the numpad +/- keys to switch audio tracks.  I don't understand why 
there are 2 tracks, and why one is silent.  OK, the fix is easy, but I 
worry that a scheduled recording might end up with no sound due to this 
(or does it record both tracks anyway?).

Extra Info...

I am using a TwinhamDTV Mini Ter DVB-T card, so audio comes in digitally 
- not from a sound card.  It is the only TV card in my system.

Myth is 0.18.1-2 I think (how do I verify this?) installed from rpms.  
System is Mandriva 2005LE.