I will post our findings here as well in case the community encounters the same issue:
The issue with entering edit mode is caused by the WPF 3.5 ControlTemplate Triggers and we already fixed it. The fix will be available with the next internal build and the Q2 2012 release.
The exceptions in the output, however, are still not addressed as we will need more time to investigate them. You can track their progress in our PITS
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