According to ~~this thread~~:
Posted by Microsoft on 10/13/2009 at 4:33 PM
Thank you for your continued interest in this bug. We have been able to reproduce the issue intermittently in several versions of Visual Studio running on several versions of Windows and have identified the root cause as external to VS. The Windows team unfortunately did not have time to fix this for their current release, but we are working with them to hopefully have this bug fixed for a future version of Windows. At present, the workaround (as many of you noted) is to press Ctrl+Scroll Lock, Ctrl+Break, or the Break key alone.
Again, thanks for all of the details you provided about this bug. If you have any further questions or comments, please feel free to post again here; although this issue was closed quite a while ago, I'll make sure it stays on our radar.
Thanks, Brittany Behrens Program Manager, VS Platform - Editor
This bug has been around since at least 2004 and, as of the above post in 2009, had not been fixed.