Think I found it. If I option-click near the top of the track header, it selects all the regions in the track, as you described. If I option-click near the bottom of the track heard, it makes an exact copy of the track, regions and all, the only duplicated track has everything selected. Do you get the same behavior?

Interesting! No, I get the same behavior (no duplication) no matter where I click in the header, with the relevant Preferences either on or off, at any zoom level (track height/width). I wonder if that's an actual feature rather than a version- or system-specific anomaly..? Perhaps it could have something to do with the particular Track Header Components options enabled (via right-click on any track header).. Anyway, I'm glad you found a solution, even if it is mysterious and unexplained.. ;-)