什么可能导致页面在浏览器返回时丢失其viewstate？

I have a page which the user gets shown when he wants to create a new or edit an existing document. There are two UserControls on the page. One simple DatePicker and a more complex grid. After filling out or editing the data he then can press continue which brings him to the review page where he can decide to really create or update the document or go back and change something. Going back is done in javascript with a history.back()I have a page which the user gets shown when he