I stumbled across this problem today, and found an interesting feedback page to Microsoft regarding the issue: http://connect.microsoft.com/VisualStudio/feedback/ViewFeedback.aspx?FeedbackID=105560

Workaround:

• Regedit: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\VisualStudio\8.0\AddIns
• Go into the add-in key you’re interested in disabling
• Manually set the LoadBehavior entry to 0x0