OK, so… I was wrong :-): CursorFX does have some kind of background process (some deets here: http://www.shouldiremoveit.com/CursorFX-6963-program.aspx). After uninstalling CursorFX & rebooting my laptop, the issue has resolved: I can now see my mouse pointer when it is over that line number & bookmark column.
Cheers,
Eric