Specifying the host gives the following output in the DOM
<script src="////id.mktoweb.com/js/forms2/js/forms2.min.js"></script>
This is caused by the adding "//" prefix twice which is unnecessary. Although browsers seem to workaround this faulty syntax, this is not ideal and was actually picked by broken link checker.
Add host to config, look at the actual generated DOM>
Will submit a patch later today.
Active
3.0
Code
Removing the duplicate "//" lead to Drupal's domain being prefixed which is quite strange, and probably is the reason why quadruple //// is used instead as workaround.