It's now the second time this happened to me:
(http://i57.tinypic.com/np2987.png)
I don't know what causes this but the first time it was fixed by loading an autosave. This doesn't work any more, please tell me you have a fix.
Just tried again and it works. Strange...
I encountered this Issue too, only quiting to desktop and reloading the game helped (tried to load different saves from menu screen, dosent worked).
Dont seems to be gamebreaking because I reload a save that i made after realising the blank prioritys window.
Used the same build as the TO.
Sadly I was unable to repruduce the Bug...