Thanks for the response. The use case I gave is just one of many other valid ones I can think of. For example, if you've scrolled a page and then try to close the tab or window (accidentally or on purpose), a dialog could open to ask if you really want to leave the page. Clicking "no" in this case would scroll the page and lose your place.
There are many such use cases, the general theme being "the user scrolls the active element out of the viewport, a dialog is triggered without the user's interaction with the active element or any other
:focusable element, said dialog is closed, the document scrolls 'by itself', the user is confused." Though I actually can't think of a case where you'd want closing a dialog to change the scroll position of the page, especially as default behavior.
Restoring the ''focus'' is fine and correct, but the scrolling is, in my opinion, an occasional side effect of this browser a11y logic whose possibility was overlooked in the initial feature implementation.
In any case, my opinion is that the widget should be the one that ''does'' allow the scroll, and that the default behavior should restore both the focus AND the scroll position, if needed. Other opinions are definitely welcome! Thanks again.