TextBoxchanged event kills others fires

I have an asp.Textbox in a Webform with a button.

The textbox have a server-side event Ontextchanged.

Trouble :
When the user clicks on the button while textbox have the focus and after a change in textbox, the Ontextchanged event is correctly fired but clicking on the button is not fired. The user have to click one other time on the button to fire it correctly.

Any idea ?

Regards