Adding another form on page breaks ..

I have a simple form on this page:

http://www.cvillessc.org/kickball/schedule

that allows filtering of a schedule contained in a database. When activating simplenews and giving the sub/unsub option on this page, when the schedule form is submitted, simplenews "takes over" and either subs/unsubs the user, and my original form doesn't work. Upon checking the $_POST array, nothing is there. Disabling simplenews caused my form to work again and the $_POST array was populated.

The forms are constructed ok and there is no overlap of the form tags. What could be the issue?