This is also true of all old migrated posts, you can’t just copy/paste expressions anymore.
That is indeed an important bump in the road for us to fix. I have taken note of it, and will bring this up to the COW developing team. As we explore further into the nature of The COW’s new platform, we are excited to be able to refine and improve our new environment. This was our original inspiration behind making the grand switch, so we hope to be able to fix this soon.