This was talked about in the discussion group here, here, and here. You're going to have to update to FogBugz 7 to get rid of this problem (I just tried it with version 7.2.16 and it doesn't exhibit this bug). It has something to do with IE8's Compatibility View (see that last discussion group post to which I linked).
One thing I discovered when I first came across this problem was that, if you navigate to your FogBugz site via its IP address rather than its computer name, it behaves properly. So, if upgrading to FB7 is not an option right now, you could try that. Better yet, switch to Firefox (in which this was never a problem).