A small example:
Let b = B in
< B > , < b > , < a > , < C > (with a < b < c)
After one cycle the sequence is sorted but the order of B and b has changed:
< a > , < b > , < B > , < c >
But you can however implement Selections Sort stable if you, instead of switching, insert the minimum value. But for that to be efficient you should have a data structure that supports insertion at a low cost or otherwise you end up with quadratic complexity.