Web Forms :: Datetime Storedin Viewstate Changing Its Format On Button Click

I am fetching date from oracle and putting it into a textbox. That textbox is takin value as dd/MM/yyyy format by default. Then I am storing the value in a viewstate.

There is a submit button on the page at clicking of that I am passing the viewstate to a function with explicitly converting it to the datatable.

When I click on the submit button for the first time. View state is capturing date in dd/MM/yyyy format and everything go on well. After the button click event completed.

Now if i agaian click on the submit button then viewsate is having date in MM/dd/yyyy frmat. Dont know how it is getting changed. Due to this format change I am facing issue in my bussiness logic and data access.