Radix Without Stability

This counting sort produces a correctly ordered output, but it walks the input forwards:

def counting_sort(A, key, u):
    C = [0] * u
    for x in A: C[key(x)] += 1
    for v in range(1, u): C[v] += C[v-1]     # C[v] = count of keys <= v
    B = [None] * len(A)
    for x in A:                              # forwards
        C[key(x)] -= 1
        B[C[key(x)]] = x
    return B

It is used as the per-digit pass of a two-pass LSD radix sort on [21, 11, 12, 22]: first by the ones digit, then by the tens digit. What comes out?