CAF Session beans with expireWithPageFlow true


we have a problem with session beans and expireWithPageFlow attribtue set to true. Session in our application is set to 4 hours. It is set in application war as well as in portlet.war and value is the same in both places.
However, if we go into the application, then leave it alone for 1,5h (it doesn’t reproduce after 1h), then session beans are invalidated and next request from the browser causes an error. I have debugged this, and I can see that bean instance is different after this 1,5h of inactivity:

and this is after 1.5h when I select a value from the dropdown (which triggers ajax):

Why are those beans gone? Is there a setting for page flow expiration time, that we should align with session timeout?
We are using CAF in version 10.1