subscribe form problem

I want to add a very simple html form to a page, to allow people to sign up for a newsletter. I’m using Campaign Monitor to send the newsletter and manage the subscriber list. I used CM’s utility to generate the form, which works fine when tested on a static html page.

<form action="https://zzzzz.createsend.com/t/r/s/zzzzzz/" method="post">
<div>
<p><label for="name">Name:</label> <input type="text" name="cm-name" id="name" /></p>
<p><label for="zzzzzz-zzzzzz">Email:</label> <input type="text" name="cm-zzzzzz-zzzzzz" id="zzzzzz-zzzzzz" /></p>

<input type="submit" value="Subscribe" />

However, when I add the form to a WordPress page and test it, nothing happens. Specifically, the data entered into the name and e-mail fields isn’t sent to Campaign Monitor, and instead of being redirected to CM’s standard “thank you” web page, I’m redirected to URL made up of my domain name plus a string of characters taken from the form data:

https://mysite.net/?s=&cm-name=name&cm-zzzzzz-zzzzzz=name%40mysite.net

I see that there is a Campaign Monitor plugin, but that would force me to use a widget and I need to have more control than that over where this little form appears, so I’d rather not use it.

I might also note that the other forms used on the site (search forms and an e-mail form built w/ Contact 7) are working fine.

Any ideas why WP won’t let the form data be sent to the external URL? Could the problem be that method="post" instead of “get”?