I have now taken a video of the issue on a machine that exhibits the behaviour - view it through the link below:
It seems to be restricted to Windows XP Machines (SP3) running either IE6/7 or 8. Have not tried IE9 on any of these machines yet.
It does not exhibit the behaviour using Firefox or Chrome. Have not tested in Safari.
I am assuming it is a configuration in IE because not all of the machines in our office running XP and IE7 show the problem.