Can you confirm exact reproduction steps for this? I believe the fix we implemented previously worked, but was incomplete.
For example, if I upload using the "Attach files" button, it seems to work fine.
If I upload using the "Insert image" button in the editor, I can reproduce the bug.
Similarly, if I drag and drop an image into the editor, I can reproduce it.
I think, actually, it's any direct uploading via the editor that causes it. Pasting an image file in does it too.
Is that consistent with your findings (I just don't want to miss anything).