Hopefully the clarifications will tell you whether or not it can be considered a bedroom. However, in this market, and with the buyers who are looking in this area, a home office is definitely "hot" while a 5th bedroom is "not." Larger homes (read: more bedrooms) are not in as high a demand at this time.
I would highlight it as a first floor office, with possible reference as a fifth bedroom. Staging it as a "model home" office will also help, as that is what buyers are really looking for.
Prudential Starck Realtors