What you described is called Sequenced method calls.
When you set a behavior on a method call, it is valid for all the calls to that method from that point and on.
However, if you set multiple behaviors on the same method, you create a sequence in which the first behavior set is valid to the first call, the second one is valid to the second call, and so forth.
The last behavior set is valid to the n-th call and all calls from that point and on (n is the number of the behaviors that you set on the method).
For instance, in your example, the first call to MyObj.MyStaticMethod() will return 0, and the second call to MyObj.MyStaticMethod() will return 1.
Any addition call to MyObj.MyStaticMethod() will return 1, for it is the last behaior that was set.
You can find more information in Isolator documentation