Hello All,

I am using command button to perform an ajax call.

Please find the code snippet below
Controller:

public with sharing class TestController {
     public TestController(){
         this.flag=true;
         ApexPages.addMessage(new ApexPages.Message(ApexPages.Severity.Info,'Loading Constructor : '+String.valueOf(flag)));
     }
     
     public PageReference changeFlagValue(){
         ApexPages.addMessage(new ApexPages.Message(ApexPages.Severity.Info,'Value Before Change : '+String.valueOf(flag)));
          if(flag){
             flag=false;
         }
         else{
             flag=true;
         }
         ApexPages.addMessage(new ApexPages.Message(ApexPages.Severity.Info,'Value After Change : '+String.valueOf(flag)));
         return null;
     }
     
     public PageReference displayFlagValue(){
         ApexPages.addMessage(new ApexPages.Message(ApexPages.Severity.Info,'Current Value : '+String.valueOf(flag)));
         return null;
     }
     
     public Boolean flag{get;set;}
}

<apex:page showheader="false" sidebar="false" controller="TestController">
<apex:form >
<apex:commandButton action="{!displayFlagValue}" value="Display" rerender="pageMessages" />
<apex:commandButton action="{!changeFlagValue}" value="Change" rerender="pageMessages" />
<a href="http://google.com">Move</a>
</apex:form>
<apex:pageMessages id="pageMessages" />
</apex:page>

Command Button : Changes the value of Flag.

Constructor : Reinitializes the flag value to true.
Steps : 
1. Load the Page.
2. Press Display : Shows true
3. Press Change : Shows false
4. Click on Move : 
5. Press Browser Back Button.
6. Constructor Loaded : Value Reset To True
7. Press Display : 
Ajax call using last value before moving to Google Page, But in controller flag value is changed.

Can any please tell me the logic behind this behavior.
Thanks