As mentioned in a previous discussion by calibas, PHP.net has this disclaimer: "Note: Under Apache 2, you must set UseCanonicalName = On and ServerName. Otherw

As mentioned in a previous discussion by calibas, PHP.net has this disclaimer: "Note: Under Apache 2, you must set UseCanonicalName = On and ServerName. Otherwise, this value reflects the hostname supplied by the client, which can be spoofed. It is not safe to rely on this value in security-dependent contexts." So it seems to be clearly a Word Press issue.