Do the following:
Open a non-RAW image (jpg, png ...).
Open a RAW image, develop it and copy it to the clipboard: Ctrl+A > Ctrl+C.
Paste the image from the clipboard into the already opened non-RAW image (step 1.).
Go back to the RAW image.
Result: The image content has disappeared, as if I had not copied but cut. The (empty) layer itself is still there.