This is, as Harold says, an interesting and difficult case. The criticial fact in this case, it seems to me, is that the copying in question was done from the purchased, copyrighted version instead of from a copy tracing its origin to physical copies of the public law. I see no contradiction in saying that the work in question here is simultaneously copyrighted and in the public domain.
Copying is the act of taking a specific copy and replicating it.
If two authors independently created the same poem, you'd have to ask permission from the one with the rights to the copy you are looking at.