Confirmation mail sent but user already subscribed to list


I use the following code for a custom subscription form:

<form class=".form-inline" method="post" action="" name="subscribeform" accept-charset='utf-8' enctype='multipart/form-data'><input type="hidden" name="formtoken" value="965eca70472facbdcebb06bada0f1dca" />
<div class="form-group">
  <label for="email">Email *</label>
  <input type="email" class="form-control" id="email" required="" name="email">  
</div><input type="hidden" name="htmlemail" value="1" /><input type="hidden" name="list[5]" value="signup" /><input type="hidden" name="listname[5]" value="My List Name"/><button type="submit" name="subscribe" class="btn btn-primary">Subscribe to my List</button></form>

The user gets the confirmation email but the problem is, that he is already subscribed and active to the list without the need to click the confirmation link in the email.

I guess I have some auto subscription somewhere…

what version of phpList do you use?