moss 2007 postbacks creates issue in URL rewriting?

Question

I have implemented url rewriting using for moss 2007 site using iis url rewrite module everything is fine.

but i also have some dropdownlist controls on my page which is required to retireve data from list dynamically. when i do postback my URL structure breaks and adds .aspx at the end of page like

http://example.com/opinion/news/the-news to http://example.com/opinion/news/the-news.aspx which gives a 404 error how can i handle this. i know about

Form1.Action=Request.RawURL;

but how can i implement in sharepoint which has it's own masterpage.