UI hangs when deleting a file from Assets

Deleting a file from within Assets is effective but the UI stops responding after clicking OK on the confirmation dialog.

Steps:

• log in to the CMS
• navigate to the Documents
• click on Assets
• on 'hippos' do Add File and select any file to be added to the folder
• click on the added file name to see the details of it
• choose Document Actions -> Delete
• click OK to confirm

Results:

• exp: operation executed, dialog disappears and the deleted file is no more visible in the UI
• act: operation is executed, but dialog remains and must be dismissed using the [x]
  back to the main screen, hit F5 to refresh the display and observe an HTTP 500 reported by the browser with this URI http://<HOST>:<PORT>/cms/?wicket:interface=:1::::
  an exception is raised and I have attached a few lines of it

Workaround: truncate the url to http://<HOST>:<PORT>/cms and hit F5

Note: the History reports the deletion of the file as well as, prior to that, the creation of the folder that contained the mentioned file. But that folder was not created at that point, so its report is erroneous.