Not able to add image to overlay text

Problem/Motivation

The background image with overlay text has a lot of blank space in it, so to improve the look of the page, I wanted to place an image with a transparent background there. The intent would be for the user to scroll past the overlay text and image and to the content.

Unfortunately, when I add an image there and save it, it says it saved successfully but no image is displayed. When I go to edit this, the image isn't there any more. I attempted to upload it as an image, and to import it as a media image, but regardless the image disappears as soon as it is saved. When I add it to the actual page content, the image does show, but it appears below the overlay in the page content area.

I found this issue → where a user asks why there is an overlay text field when the page content could provide this, and the answer was that this was to decouple the page content from the overlay text. In that case, I wonder if being able to put an image in should work and this is a bug.