Button not activated after type

Hello,
I encountered an issue with Selenium.
I type something in a text box who is in relation with a button.

In normal case,user, the user type into the text box who detect that something has been written in, so the button is activated.
But with Selenium, the button not activated, the detection of the text box seems to not work with the "type" method of Selenium.
Do you have any idea to resolve this issue.
Regards,

I suppose you face this (and many more) such issues because of using Selenium1 API. If you move to Selenium2 API you may get rid of this issue