Wave Volume control Using GT4

I was going  to upgrade from GT3 to GT4 a few months ago on my  Windows XP SP3 machine. I immediatedly noticed I couldn't control the volume unless I first minimized GT4 or opened te master volume control panel. Using GT3, I can increase or decrease the volume without miniimizing GT3 or opening the volume control panel.
 
It is important for me to be able to change volume "on the fly". I use Guitar tracks mainly for backing tracks I have recorded and sometimes I need to adujust the volume. I use a foot switch I have designed that will start/stop, and control the volume in GT3. I cannot vary the volume with my switch or manually in GT4 unless I do the minimize GT4 first.
 
The Volume control does not respond in GT4 unless I first minimize GT4 or open the master volume control panel. Is this the way it is or am I missing something?