Weird, but it worked for me. (At least so far.) I noticed in the developer console there were a few errors reported for "crisper.js" and clicked to expand those errors. Then I closed the developer window, and refreshed the page. Still it did not work.
Then I noticed the URL was opera://settings/content/cookies?search=cook (because I had searched for the section in the Advanced settings area.) I removed the querystring parameter and viewed opera://settings/content/cookies and tried again... Then it worked. I'm not sure if the querystring was confusing the call to the JS or not, but I was able to add a new domain to the "Clear on Exit" list.
Thanks for the suggestion!