pfSense

Please note that the default webpage generated by get_default_captive_portal_html() /etc/inc/captiveportal.inc with a POST form to submit a voucher, doesn't submit when user just hits "Enter" in MSIE, one needs to click the Submit button. This might confuse some users. In other browsers, pressing Enter submits the voucher code as expected.

There is some discussion on the Web about MSIE being picky, when one wants to submit a form, like a login or search, just by hitting enter:
http://www.thefutureoftheweb.com/blog/submit-a-form-in-ie-with-enter
http://www.google.com/#&q=msie+html+submit+a+form+with+enter&fp=1