I recently tried to rollback a revision of this post
However, when Jon Ericson tried to do it he was able to.
I've been unable to reproduce this on another post and there were no pending suggested edits.
I've got Firefox 23.0.1.
Niall C and I are able to reproduce this on the following post attempting to roll back to revision 2:
In both cases, there was a suggested edit on the post which was "improved"; rolling back to the version from the suggested edit fails.