This phenomenon is explained at the link:
but I have not seen this explained. The reason the test fails is that the array from which the max element is being sought has repeated max elements, so there are two possible indices to return. I suspect that the spec for icamax does not require, for example, that the smallest index of the max element be returned. The test expects index 2, but some implementations of blas return index 3, for the two test cases.