Siebel adding charset utf-16 to header for soap calls

We have version 21.1. I've tried looking around on oracle support and various docs to figure out why Siebel is adding charset=UTF-16 with no luck.

We're calling a service using SOAP with EAI HTTP Transport business service, SendReceive method.

httpInputs.SetProperty("HTTPAccept", "text/xml");

httpInputs.SetProperty("HTTPUserAgent", "useragenthere");

httpInputs.SetProperty("HTTPContentType", "text/xml");

httpInputs.SetProperty("HTTPRequestURLTemplate", url);

httpInputs.SetProperty("HTTPRequestMethod", "POST");

When this code runs, Siebel keeps slapping on UTF-16 to the content type causing the receiving API to not know what to do. Is there a way to stop Siebel from adding this? I tried changing the code to force UTF-8 and that seemed to stop it from making it utf-16, it became utf-8 instead but the API didn't like that either.