Track Envelopes Don't Work On Playback ~ Sonar X3b

I'm using Sonar X3 Producer and have applied the X3b update.
 
I've added an 'Automation Lane' to three audio tracks each with a volume track envelope. Only one track is playing back the envelope. The other two tracks ignore the envelope and playback at the set track slider setting. The 'Read' button is on for all tracks.
 
If I manually drag the cursor line across on the time line, the sliders follow the envelope parameters. Also, if I delete the working track, then one of the other tracks will read the envelope on that track on playback.
 
It seems I can have just one working track envelope at a time in my project! I should add that I've never had any problems using envelopes with previous versions of Sonar.
 
Can anyone offer any suggestions.
 
Thanks.