RESTEasy appends "charset=utf-8" to OutputPart's content-type "image/png" or "image/jpeg" for multipart/form-data requests

When I call a REST endpoint with content-type "multipart/form-data", then JBoss alwas appends ";charset=utf-8" to the content-type of a part, not only for text-based content-types, but also for binary e.g. "image/png" or "image/jpeg".

Problem is now, that the receiving .NET application has problems interpreting InputParts with content-type e.g. "image/png; charset=utf8".

Is there a way to change this behavior?