sequence d.: missing multiple layers of activation

[matthias]

Assumed one class with method M1 which calls method M2 of the same class
--> in a sequence diagram I find one lifeline with multiple layers of activation
(see helptopic "Lifeline Activation Levels")

now an analog example with TWO classes: a method A.M1 of class A calls method B.M1 of class B which calls method A.M2 of class A which calls method B.M2 of class B etc.
--> I expect two lifelines (classes A and B), both with multiple layers of activation like above. However, I cannot see the multiple activation layers in this case!

My mistake or the mistake of EA ?