Just noticed, Nigel, and thought I should mention it in case it helps …
Mtcrosoft’s Edge browser handles the situation somewhat differently (What I reported yesterday was the way in which my normal browser – Chrome – handles it). In Edge, after clicking ‘Save’ following the image upload, the user receives the message:
The site you’re on is trying to close this tab. Do you want to close this tab?
Options: Yes or No. Clicking ‘Yes’ returns the page to which the media object was being added and the ‘close button’ page is not presented. Neater than Chrome (although not enough to convince me to change browser!)