Dropdown autopostback problem with browsers back button

I have 3 dropdownlist

First dropdownlist is pulling categories when i select a category from ddlist 1, I fill second dropdownlist with sub categories of a category which i selected on ddlist1.

Wh开发者_如何学Pythonen i selected a sub category from ddlist2 i fill the third ddlist with products.

When i select a product from ddlist3 its redirecting me the products detail page.

If i press back button of the browser and select another category from ddlist1, ddlist1's selectedindexchange event firing after this event worked something is triggering ddlist3's selectedindexchange event even i dont touch ddlist3.

Note : I am clearing items in the ddlist2 and ddlist3 on ddlist1's selectedIndexChange event.

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When you clear the items, does the ddlist3 index reset to 0? This change can fire the SelectedIndexChange event.