Textchanged Event is not fired?

Hi,
I have one DropDownList,2 TextBoxes.Each TextBox has TextChanged Event.
When i select DropdownList,enter a value in first TextBox,Then concern second TextBox values is present.
Another senorio is DropdownList selected,When i enter second textbox concern first textbox  value is Present.
I checked both operations one after another.
Now DropDownList is Selected,When i enter First Textbox it did not get value for second TextBox.It did not fired after i did above operations
Whats the problem ,i did not find?
Thanks,
Rama Krishna
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