Strange Frobenius norm of a certain matrix

Dear All,

Consider the following code:

(%i1) A:matrix([1,1],[1,1]);
                                   [ 1  1 ]
(%o1)                              [      ]
                                   [ 1  1 ]
(%i2) mat_norm(A,frobenius);
(%o2)                                  4
(%i3)

Should not the Frobenius norm of this matrix be equal to 2?

Thanks in advance,

Paul