HTML Form Submit Behavior

Long no see and write this blog!
I think i have much time to record my knowledge and testing.
That time i want to talk about the html form submit.
It make me feel confuse in IE( I test it on IE6).

Behavior 1 :
When form only have a single input text field, and user press enter button, it will directly submit the form.

Behavior 2:
When form not only have a single input text field, and user press enter button, it will acting click submit button to submit the form.

you can simple test this behavior, you only need to add a javascript on