1. Create a new chat window by double clicking a contact, for example Rupert
2. Confirm that if you right click the contact tab label you get a menu that reads "(icon) Rupert"
3. Create a new chat window by double clicking a contact, for example Banana
4. Confirm that if you right click the contact tab label you get a menu that reads "(icon) Banana"
5. Drag and drop Banana's tab to Rupert's window

Expected:
Tab label right click menu says:
  (icon) Rupert
  (icon) Banana

Actual result:
Tab label right click menu says:
  (icon) Rupert
  (this label is blank, but there's a menu item)

The following is printed to the console:
(empathy:9448): Gtk-CRITICAL **: gtk_selection_data_set: assertion `length <= 0' failed

Screenshots attached