lxc-copy -e creates an ephemeral container, which means that it is deleted when it stops. If I understand the man page correctly,
lxc-copy -e -D creates an ephemeral container that is not deleted when it stops. So it is persistent (and the term ephemeral seems to be misleading).
I created two snapshots with
lxc-copy -e -D and
lxc-copy -s, and compared their config files. The only differences were the MAC addresses, rootfs paths, and utsnames. Both snapshots persisted after stopping them. Which leads me to the question:
lxc-copy -e -D different from