Dragging tabs in Tahoe Safari is broken.

I upgraded to MacOS to Tahoe. In Safari, I want to combine two windows into one window with two tabs. So I drag the title bar of one window to the title bar of another. As in previous versions of Safari, this combines the two windows into one window with two tabs. But unlike before, it leaves behind a separate window with the Start Page. To recap: I start with site A in window 1 and site B in window 2. I drag site B to window 1. Window 1 now has two tabs with sites A and B. But window 2 remains open, showing the Start Page. I have to take the extra step to close that window. Is this a bug?