Yeah, it appears that's not working right. After applying the thumbnail change, you'll see that it gets applied if you drag the speed dial around as it'll show the change while the speed dial is in the drag state. It just won't show in the normal state.
I also got a speed dial suggestion for https://static-00.iconduck.com with the correct thumbnail on it. Might be where Opera gets some of those backgrounds and they're just not applied right.
Definitely sounds like a bug.
