I just had a similar experience while trying to book a site at Tallulah Gorge SP, GA. We want a site with 30amp power. Every time I set my search parameters to 30amp the results showed none available. Revising the search to 15amp displayed several sites available. When selecting the type of site preferred, GA is non site specific, it was displayed as having 30 to 50amps. Frustration led me to call the 1-800 number. Explained my dilemma and was told "Oh yes, all those sites are either 30 or 50amps. The web site is just messed up!"
Who'd a thunk.