Based on your guys responses I played around with PT and I found the way I get into this problem.
If I turn on both 'Link Timeline and Edit' AND 'Link Track and Edit', and then select a timeline section, all the tracks will be selected.
Now if you turn off the same two 'Link ...' buttons, then all of the tracks are still selected, but you can't unselect them. There is no unselect all tracks button that I can find.
I see now that if I just leave the 'Link...' buttons engaged then I don't get stuck like this.
Well, I am still getting into all tracks being selected when I don't want it sometimes even with both buttons in. Can't figure out what the key reason is.