Popup window Problem

Popup window Problem

Hi,
 
I have a Scenario.:
 
If I Open a Page twice in diffrent tabs. 
The page have 'Add Item' button. When clicks, It will open a popup window. Which adds Items from Popup window to respective Parent Windows.
 
But when I open same url twice and click on Add Item button on respective pages, Items are getting added only in first window. and not in second window.
 
 
Thanks and Regars,
Gauri Rane