Originally Posted by ProDigit
The issue is, what stops someone from copyrighting a public domain creation?
Simply the very definition of "public domain". Nobody can copyright the works of Charles Dickens, for example - they are in the public domain.
What you can of course do is add something to a public domain work, and then you will hold a copyright on those portions that you have added. Eg, many scholarly editions of the work of Dickens have introductory essays, explanatory notes, etc. Those are copyrighted, even though the actual text of the novel is not.