MVC block has issue with form not submitting - php

Question

Just some background. I'm using an MVC. My form is put in a div in my template. It posts to the same page where my controller catches it with an isset(), saves stuff to the database, and redirects to a welcome page.
EDIT: It posts everything like it should if I remove the action part of the form. Must be something pertaining to the way index.php reroutes it to ensure that the user has permission to go to that URL, etc. Still looking for a solution.
I've done some debugging and it is apparent that the variables are not showing up in the $_POST variable.
<form method="post" action="<?php echo BASE_URL; ?>/login/register">
<fieldset><legend>Person Info</legend>
<table>
<tr><td><label for="firstname" class="required">Firstname:</label></td>
<td><input name="firstname" id="firstname" type="text" value="<?php echo $firstname; ?>" /></td>
</tr>
<tr><td><label for="lastname" class="required">Lastname:</label></td>
<td><input name="lastname" id="lastname" type="text" value="<?php echo $lastname; ?>" /></td>
</tr>
<tr><td><label for="email">Email:</label></td>
<td><input name="email" id="email" type="text" value="<?php echo $email; ?>" /></td>
</tr>
<tr><td><label for="username" class="required">Username: </label></td>
<td><input name="username" id="username" type="text" value="<?php echo $username; ?>" /></td>
</tr>
<tr><td><label for="password" class="required">Password:</label></td>
<td><input name="password" id="password" type="password" value="<?php echo $password; ?>" /></td>
</tr>
<tr><td><label for="pass2" class="required">Confirm:</label></td>
<td><input name="pass2" id="pass2" type="password" value="<?php echo $pass2; ?>" /></td>
</tr>
</table>
<button type="submit" class="btn btn-custom-lighten">Submit</button>
<button type="button" class="btn"
onClick="parent.location='<?php echo BASE_URL; ?>/nonprofit/welcome'">
Cancel
</button>
<br>
<br>
<button type="button" class="btn btn-primary"
onClick="parent.location='<?php echo BASE_URL; ?>/nonprofits/register'">
Nonprofits Register Form
</button>
<br>
</fieldset>
</form>
You can see my names are consistent from the controller code.
public function register()
{
print_r($_POST);
if (isset($_POST['firstname'])) {
try {
$person = new Person();
$person->handleUpdate($_POST);
$person->setUsername($_POST['username']);
$person->setPassword($_POST['password']);
$person->save();
header('Location: '.BASE_URL.'/login/welcome');
exit();
}
catch (Exception $e) {
$_SESSION['errorMessages'][] = $e;
}
}
$this->template->blocks['content'][] = new Block('registerForm.inc',array('return_url'=>$this->return_url));
}
Any help would be appreciated, but it looks to be an issue with my form. My form does get rendered, it just doesn't submit.