Why Reset button does not work more than once in ASP.NET web application

With ref. to ASP.NET web application: suppose there are two textbox (web form controls) , one reset button(HTML control) on the screen. when the page is loaded for the first time,I enter some values in two textboxes and press reset button. Values from the text boxes gets cleared on clicking the reset button. If I perform the same activity again reset button doesn't work.