We have noticed that when a portal loads the URL for the entry tab (T1) doesn't contain the param NavUpdatePath. However if you navigate from the entry tab to the second tab (T2) it adds a param NavUpdatePath=false to the URL. If you hit the browser back button to navigate from T2-> T1 it works perfectly and the browser executes a GET request. However if you are in T2 (from T1) and navigate to T3, this time also it adds NavUpdatePath=false to the URL. But if you want to move from T3-T2 using the bowser back button its a POST request and it thows a page expired error after popping up a http-https alert window (we are absolutely sure that all the contents are https in portal).
The question is why it adds the param 'NavUpdatePath' in the URL for T2 and T3 and why moving from T2->T1 it is a GET request and T3->T2 is a POST request? What is the significance of this param, in which API it is used?