Highlighting in full screen, wrong text highlights

One of our instructors is having problems highlighting in full screen. He selects text to highlight but text further down highlights instead. He's been doing this for almost 7 months now, and this is the 1st time it's happened, and it happens on both his laptop and desktop. I remade the file for him, and it worked fine on his laptop (pdf annotator version 7.1.0.726), but not his desktop (pdf annotator version 8.0.0.803).

I saw another thread about highlighting problems that was close but not the same, and it said holding the shift key down before selecting text to highlight might help, so I'll have the instructor try it, but does anyone else know any solutions to this?

Thanks!