ModalDialogBox Posting only 3 times.

Hi All,
I have ASP.Net 3.5 site.
I Have a Modal Dialog Box in my site which is posting back through a ASP Button.
Whenever I click on the buttton in the modal dialog, I do some action on server side event.
But the postback is happening only 3 times. From the 4th time, it does not make a postback to server.
I learn that Modal Dialogs are not meant for postbacks and we should not use them for it, but my question is why does it postback 3 times and why it stops after that.
Note that, while opening this dialog, I am using a random querystring to avoide caching of modal dialog.
 
Thanks.
Jimmy.
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