Take a look at Chicago Manual of Style (15th edition) section 7.90, and you'll notice that all but very
few prefixes are joined to root words with no hyphen. Many writers are reluctant to close up prefixes to root words.
Maybe it's that they think a word looks too long and unreadable when a prefix is joined with a root word. Or maybe
it's that they've seen hyphens or open spaces in other publications, so they think that it must be right to do
it that way. But the next time you use a prefix, consider the rules: What does CMS say about it? Also check
for the word in the dictionary. Many compound and prefixed words appear in m-w.com.
All of these examples, as strange as they might look, are correct:
Superset (n; not super set)
Re-flex (to flex again)
Re-create (to create again)