I now believe this is definitely an oversight.
I find if I set the selection start and stop points with the Selection Module in the Control Bar on the Time Line to select the time range, tracks don't unexpectedly get selected. However, if I use the mouse to select the time range on the Time Line, ALL tracks get selected.
Very inconsistent. Previously, either way would not change the tracks that were selected (which fits my workflow much better). My opinion is that SONAR should not be making the assumption that I want to select ALL tracks if I make a selection using the mouse in the Time Line. The Time Line should be used to select time, not tracks.