I think I have worked the bug out, obviously I don't know how to resolve.
If I click "highlight" and choose players best position - when I jump around players it works exactly as it should (position selected). If I then click "highlight" again the selection goes off, and its then on last played position, I click on a position it displays, change to another player it doesn't.
So having it clicked onto players best position, which makes the most sense anyway, keeps it working.
Hope that makes sense and helps - thanks.