This "fix" was by design in x2a.
It went like so, and must have come from support via the customer base.
If you were tweaking along on the prochanel and wished to mute / solo or otherwise tweak a control
that was NOT the selected track you were looking at on the prochannel you could do so without the prochannel changing strips on you as a "penalty" for wishing another track was adjusted differently during prochannel tweakage.
You will note that this action is not limited to the volume slider, but every widget on the strip.
In short while versions of Sonar from 1.0 to X2 would select the strip of the widget tweaked,
X2a and beyond do not. You must mouse-down on the strip and not a control to select the strip and the inspector in concert.
When x2a landed it broke my control surface code. But after Noel explained this reasoning to me I realized that it was just a loop held up for me to jump through. - There's been a couple of those. I believe Craig Anderton referred to these as "tickles" to the Sonar code which have a ripple effect on 3rd parties. - editorial at no charge btw. ;-)