Using the latest Pico-8 version, if I highlight with Shift/Click a note or series of notes in the SFX editor then copy with Control/C, I can paste the result into another column in the sfx editor with Control/V but if I close the cart and open another cart to paste to, I get the message "Nothing to paste" when trying to paste with Control/V.

I have tried Linux Mint and Windows10 with the same result.
The documentation says this should work, any idea what I am doing wrong?
Thanks,
Peter