I'm not seeing that issue in VS 2012 in a simple test I made. Can you email a new simple sample project showing it to us so that we can debug it? Please rename the .zip file extension so it doesn't get spam blocked.
Adam, your issue is actually a bug we found in VS 2012 prior to its RTM. We reported it to the VS team, and back in August they said they fixed it for the first VS update which is due sometime in November-ish timeframe. The bug was that if a control exposes an ImageSource property in the Properties tool window and the project has a lot of images in the project, the lockup occurs. Since a lot of ribbon controls have the ImageSource properties in the Common Properties category, they show when getting selected in the designer and trigger the bug. Unfortunately we're stuck with it until the first VS update is out.