Thanks so much for the quick response.
Not resolved, but here’s what I’ve tried:
I disabled every plugin except Adrotate, still no joy.
Loaded adrotate in a different theme and don’t see the broken behavior.
However, I failed to mention that I’m using 2 AdRotate widgets in the sidebar. The first is displaying a single unit, fixed. The second is the dynamic version.
So then I went back to the original site, removed the static AdRotate widget and the bad behavior disappeared.
So it seems to be tied to having 2 adrotate widgets, one dynamic, one static. Could you possibly give that a go and see if the behavior shows up for you.