Just an update--
We're aware of this happening and working to get it resolved. The workaround is to instead create a new email and copy the content over if you need it. We are happy to help with this for the meantime, just let me know the name of the email you want copied to a new draft.
Is this right after you choose to make the copy or are you making changes to the campaign first? What is the name of the campaign in your account that this is happening with?