SoapVar and Case sensitivity

Hi all, I'm trying to access to a Soap web service (written in .Net) using my php server (Apache 2.4.3 Win32, PHP 5.4.7) and class "SoapClient" When I call a soap method, and see my sent data all tags names are in lowercase. Here an example : Client->MYCall(new SoapVar($this->mUserName, XSD_STRING, "string", "http://www.w3.org/2001/XMLSchema", "UserName", "http://[MY-ns]")); The resulting request : <soap-env:envelope xmlns:soap-env="http://schemas.xmlsoap.org/soap/envelope/" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:ns1="MyNS"> <soap-env:body> <MYCall> <ns1:username xsi:type="xsd:string">JhonDoe</ns1:username> </MYCall> </soap-env:body> </soap-env:envelope> If you see the UserName is in lower case in the xml request whereas I write it using capitals. Does some one has a tip for this ? Thanks in advance BR. Mokhtar