Let n ≥ 3 , n\geq 3, and let Y Y be a simply connected, simple algebraic group of type D n + 1 D_{n+1} over an algebraically closed field K . K. Also let X X be the subgroup of type B n B_n of Y , Y, embedded in the usual way. In this paper, we correct an error in a proof of a theorem of Seitz (Mem. Amer. Math. Soc. 67 (1987), no. 365), resulting in the discovery of a new family of triples ( X , Y , V ) , (X,Y,V), where V V denotes a finite-dimensional, irreducible, rational K Y KY -module, on which X X acts irreducibly. We go on to investigate the impact of the existence of the new examples on the classification of the maximal closed connected subgroups of the classical algebraic groups.