Subspace problem

 Hi, I have 2 2Dvectors that I need to compute the angle between them.
 v1 = [1; 0]
 v2 = [-1; 1]

 subspace(v1, v2) = 1.5708 which is false

 while 

 acos(dot(v1, v2) / (norm(v1) * norm(v2))) = 2.3562 which is true

Why subspace gives me wrong answer? Shouldn't it also gives me 2.3562? Can someone explains me why subspace works differently

Thanks