I think this new behaviour is a little broken / incompatible with topmost software. As soon as I grab the tab, it suggests creating a new window for it. It's no longer possible to simply move the tab inside the same window (only by returning it back from the new lister, after it was created).
The reason for that was a running WindowTop. DOpus probably got confused with its' topmost or invisible window. Could this new drag&drop behaviour be disabled?