Web User Control

Hi all,
I am creating a web user control, which will be called from different pages in our appplication. The user control will display Item Details. So, the pages will contain a list of items with limited information. When the user clicks on one of the items, the user control will display all the additional information. So, what I am doing is opening the user control using a modal popup extender, which is inside an Update Panel. I have two issues.
1. When I click the item to open the User control multiple times, a comma is added to the text boxes every time after the first time I open it.
2. When I click the item to open the User control multiple times seems to be creating a new page. In other words, If I click the back button in IE, it goes to the page itself the same amount of times I opened the user control.

Any ideas on how to solve this?

Thanks in advance.