WhenCalled is not overriden by last instruction

Hello

In some testing scenarios I'd like to override the behavior of WhenCalled().WillReturn() for the same function.
However, it seems like only the first instruction takes part, instead of being overridden by a later one.

Consider the following example:

[TestMethod]
public void CreateUsersExceptionTest()
{
Isolate.WhenCalled(() => MyObj.MyStaticMethod()).WillReturn(0);
Isolate.WhenCalled(() => MyObj.MyStaticMethod()).WillReturn(1);

Assert.AreEqual(1, MyObj.MyStaticMethod());
}

This tests fails with "Assert.AreEqual failed. Expected:<1>. Actual:<0>."

1. Is that the expected behavior of multiple WhenCalled().WillReturn() instructions?
2. If I do want to override the behavior, what's the best workaround?
If possible, I'd like to avoid calling Isolate.CleanUp().

Thanks
Yaakov