Problem with Validation when using an image submit button

[eluser]Oussama M Billah[/eluser]
Hello,

I m having a form with an image submit button.

When filling the form and clicking the submit button the form is correctly validated.
However, when i fill the form and press the enter button the form is not validated and the same page is reloaded with no error msg.

when I use a plain submit button ( no image ) everything works fine.

the only difference between the two type of submit buttons is that when using an image
I add '_x' to the submit button name in the controller.
What can be the problem that causes the form to not validate when pressing the enter button.

Thanks