normalization and eig()

if I have a stiffness matrix K and a mass matrix M, the columns of modeshapes V obtained by [V D]=eig(K,M) are all normalized with respect to M for example V(:,1)'*M*V(:,1)=1 However, for larger problem such as 700x700 matrix the modeshapes are not normalized with respect to M. And the diagonal of D is not sorted for larger problem. Why is that? Also is it possible to write codes without for loops to force normalize the shapes w.r.t. M?