Yes the issue is only with post load activity. Without the post load activity I dont see any issue.As suggested above I tried by changing the data page to editable and dont see the issue anymore even with post load activity. Thats great. Thank you.
Does this mean there are some restrictions in using post load activity for read only data page as the issue I faced seems weird.
Well I guess it depends what the post load activity is actually doing. But yes changing the content of the page doesn't seems to be a proper design here so I would recommend to try a different approach.