Are you pasting the file or the image data?

If you’re opening the image, and copying the file’s contents, I could imagine it becoming uncompressed bitmap data to be stored on the clipboard rather than the clipboard containing lossy compressed image data. When pasting the contents somewhere, you can’t count on the destination handling jpeg data as often/reliably as you can count a destination being able to handle bitmap data.

edit: I hit the wrong reply button, but I guess this stands alone fine as it is.