Multible Isolate.WhenCalled() returns the last mocked value

I'm calling same method twice but returning different value on each call.

Reader reader = new Reader();
Isolate.WhenCalled(() => reader.ReadValue()).WillReturn(1);
Isolate.WhenCalled(() => reader.ReadValue()).WillReturn(2);

Problem is that the first call already returns the number 2. Am I missing something?

I'm using TypeMock Isolator 5.1.1.0