That is actually a bug that goes back to roughly 2001
http://bugs.php.net/bug.php?id=11058
The issue is that bigmouthfuls.bangbros1.com is a CNAME rather than an IN A pointer
mcd@tsavo:~$ host bigmouthfuls.bangbros1.com
bigmouthfuls.bangbros1.com CNAME bangbros1.com
bangbros1.com A 66.230.182.98
Zend of course claims it is a bogus report, but, it happens all the way through 4.4.0 at least.
What you might do is split the url with parse_url() and use gethostbyname() on the domain portion, then reassemble the URL using the IP -- however, you will want to send a Host: header with your request in case they are using virtual hosting and have multiple domains on that one IP.