Simple. Drag an image file from Resources into a Markdown file that you’re working on in the CMS. Full bore crash that requires a Force Quit and loses anything you’ve done since last save.
There’s a lot of these Macs-should-work-like-this things that Elements doesn’t understand. What should happen in the above case, since Elements knows the filename, is insert a  into the Markdown. This would save a lot of time and typing.
But as I say, there are plenty of other drag-and-drop-expectation things that aren’t working. Do you guys want a full list?