The status of a locked document is not shown

Steps to reproduce:

1. Login as author
2. Go to a document in the Experience Manager and open it for editing (e.g. 2013 harvest in news site item)
3. Login in another browser as admin
4. Go to the document from step 2

Expected result:

There is a warning that the document is locked by author

Actual result:

No status is shown and the progress bar runs forever.