If you are selecting a considerable area on the system track, it is possible for the selection checkbox to not appear. The particular case I see is:
- In galley view, click on the system trackfor the RIGHTMOST measure you want to include in the selection.
- Scroll to the LEFT such that the rightmost measure is pushed out of the window.
- Shft-Click on the system track to extend the orange selection to the left.
- Scroll to the right to the RIGHTMOST measure in orange. It will not have the selection box displayed unless you do some additional clicking on the bar.
It is not a big deal, but would be confusing to new users.