Two related issues happening for me, one of them is game-breaking.

1)  The "OK" button on the quest popup dialogs (the ones that appear superimposed over the game map) are not clickable.  The only way to advance past that dialog is to hit Escape, and then resume game, at which point the dialog is cleared.

2)  For quests in which a dialog appears and then one is immediately put into an encounter (for example, the 2nd part of Mastery quest where you fight the giant with the hammer), the aforementioned inability to clear the dialog effectively freezes the game.  You can use Escape to get to the main menu, but it doesn't clear the dialog, and there seems to be no way to proceed past this point.  Can't select another unit, can't end turn, etc.

Any ideas?