All: This experience is VERY common at WDW...
Let me explain - there are two classes of restaurants at WDW. DISNEY OWNED and NON DISNEY OWNED.
DISNEY OWNED - you make not book a reservation in any other fashion than going thru the semi-broken
MDE site. The singular emerging exception is Victoria & Albert's.
NON DISNEY OWNED - pretty much the following:
1) Virtually anything at DTD
2) Anything at swan and dolphin.
3) You THOUGHT the restaurants at EPCOT could be done this way - Nope.
Let's go into 1) and 2) in some detail... DTD - that would be STK (when it shows up), Fulton's, Portabello, TREX, Boathouse, Morimotto's, RainForest - and as others appear? WDW does not own them.
Swan and Dolphin: Shula's, BlueZoo, IlMulano.
You may contact any of the restaurants in category 1) and 2) directly. And book them. They would, in fact, LOVE to have you call them. You do not have to keep struggling with MDE.
In addition, any restaurant at Golden Oaks my be contacted DIRECTLY, and booked.