The same applies to the "Calling the World's Maw" of my druid. Might have something to with a bonus duration calculation error. Other spells might also be bugged.
I can confirm that I suffer from the same problem.
Here's my save : https://dl.dropboxusercontent.com/u/7004246/1b05abd3-e924-4876-90f5-79e3417b5a12%20autosave.savegame