ModalPopupExtender resets TabIndex to -1

Question

After postback from Modal Popup Extender all controls tab index set to -1, i am not able to find any solution for this, And there are more than 60 controls in my page.
How i can keep the Tab Index of all my controls in ASP.NET page?
In our module we are using 4 modalpopupextender.
Case 1: When Parent popup open all tabindexes work fine, even when click on child popup  which open on the click of small button of parent popup still tabindexes of child popup works fine. But when I click on button on child popup it resets tabindexes of child popup and controls on main page.
Case 2: We are using  Separate Popup for Confirm messages , on click of button in grid we shows popup on screen in this case tabindexes are not working properly
Case 3: As said above in Case 2 , We are showing Confirm popup for deleting records  in grid in this case as well tabindexes are not working.
Please provide the solution asap. 
Please find the below link for your reference.
You will find nested popup file in this link. In this file open first popup and after that open second popup. press tab button. It will redirect to address bar url instead of textboxes in child popup.
https://drive.google.com/file/d/0ByWzy3nn7aT_bnZtOWcxbVZnVnc/view?usp=sharing