Iphone: virtual keyboard is not hidden after recording / pressing the "Go" button

I have a form with an input field and a submit button. Nothing special here ...

On the iPhone (iPhone 4S, iOS 5.1), I use the virtual keyboard to fill in the input field, and when I press / press the Go button on the keyboard, the form is submitted. But the virtual keyboard does not hide after sending.

If I use the submit button, the keyboard disappears. This problem only exists when you press the Go button on the keyboard.

Are there any javascript events that I should check? Or do you have a hint of me?

Btw: In other forms with the same structure, this problem does not exist.

Thanks at Advance