Filter Criteria "Workbench Moderation: Current" only works on published revisions?
I found the answer in this post: https://drupal.org/node/1947732

From that post:

"The key is when you create the view, you need to set it to show content revisions rather than content. They mysql query used when showing content revisions is different than when showing content. One pulls data from the node table, the other pulls from the revisions table. The latter is what you want when dealing with revisions. In my testing so far, the Workbench Moderation: Current filter works fine in a content revision view."