Interesting, I did test CS4 as well as CS5, and did not have an issue. I will note in the bug though that you encountered the problem in CS4.
my code is testing for any form post.
your code is testing for the button named "Send" being pressed.
I was sending generic code just to give an idea, your code is more specific to your form.
Really, either will work, though yours would probably be the better choice since it would keep the session from being reset in the instance where there are more than one form on the page.