It is how Drew has pointed out, the castling rights given in any FEN are not the current castling capabilities in the given position, but the availability for this position according to the castling rules. "KQ" means that neither the King nor the two Rooks has lost the castling rights. If only "K" is given than you can conclude that the white Rook on kingside has moved or is captured, but the King has not yet moved.
The castling rights inside the FEN are not affecting the castling rules. Even if the King is in check, the FEN has to give the castling availability, because the King will not loose the castling right until he has not yet moved, independent from the current castling capability. The exact FEN rules are given here: http://kirill-kryukov.com/chess/doc/fen.html Gregor
