I don't think this is going to be a bug exactly but we'll likely need steps to reproduce it if it's something you can reproduce consistently.
I'm 99% certain that the image in the post will be coming in as a data URI encoded string instead of the URL of an image or instead of attaching the image data as a file based on the paste data.
And it works fine here, however, at the time I remember thinking it odd that the attachment thumbnail had the extension jpeg, instead of jpg (which it is.