Here's a question posed to me many a moon ago: Do you have the legal right to file a treatment/concept with the WGA using CBS's intellectual properties? The argument being that since you used their intellectual properties in a registered work that you are laying copyright claim too, that you are in a roundabout fashion, claiming to have a stake in their copyright. Which could be viewed as a violation of their copyright; seeing as your were not employed to create the work.
Same sort of legal gray area as fanfilm and fanfiction.
Yeppers. Some of the same claims to, IRC.