Hi Mark L,
I've faced this bug earlier today. Just like you described, I could not un-pause the game after the duc was killed. After several alt-tab/force quit/reload I unchecked all of my auto-pause checkboxes (in my case that was Enemy spotted, Combat Start and Spell cast). Turns out it solved my problem. The game no longer pauses during the event, therefore solving my problem.
I hope this will solve it for you as well.
ps: This was with patch 1.06 on Steam