Confirmation message not showing when I change button to an image

Hey folks!

I've been playing around with the Subscribe to email plugin. It seems to be what I'm looking for (I'll list below a couple of enhancements I think would work well).

I have the form showing in a couple of places in my theme (without using the widget), and I have also modified the form output to suit (I know I'll need to change this on every update, but thats OK for now).

One thing I have done is change the form button from a 'button' to an 'image'. All works well, apart from it now doesnt show the ajax confirmation message, and instead just reloads the page. The email address has been added to the system though.

I'm sure it's a simple fix. Any help would be appreciated!

Here is my code:

function subscribe_by_email_form_home() {
	$content = '';
	$content .= '<form>';
	$content .= '<div id="subscribe-by-email-msg"></div>';
        $content .= '<input id="subscription_email" name="subscription_email" class="emailfield2" maxlength="50" value="" onfocus="this.value=\'\';" type="text">';
	$content .= '<input type="image" src="images/button-signup.png" style="vertical-align:middle; margin:0 0 3px 6px; width:54px; height:23px;" class="button" name="create_subscription" value="'.__('Create Subscription', 'subscribe_by_email').'" style="width:99%;" onclick="SubscribeByEmailCreate();" />';
	$content .= '</form>';

	return $content;

I've played around with it, and it is only the input type being 'image' that is causing it not to work.

The enhancements that I think would work well are:

1) Email opt-in confirmation
2) Ability to un-subscribe via the same form