Textbox value gone when postback occurs

Question

Hi all,
I am having ajax tab container and gridview in each tab. Gridview contains columns in which one column is dropdown box and another column is text box.
In page _ Init ,Tabs are added to tab container and in pageload gridview is created inside each tab.
If user changes the dropdown value and enters some value in the textbox before the postback of drop down is complete, due to reload value entered in textbox will vanish.
Is there some way to prevent user from entering the value in textbox column before the postback of dropdowncolumn is complete?
 
Regards,
Simi J