Following post has information about the problem:
http://forums.asp.net/post/5219096.aspx
I have tried to repro this and as the user mentioned, this happens on selfhost but works fine on webhost.
Comments: As mentioned above, the issue here is that HttpClient does not understand UTF8 in headers. This is not part of the MVC/Web API project. And we did open a bug against HttpClient to allow for UTF8 as a fallback. However sending non ASCII characters in a header is going against the http spec, and is going to randomly break you EVEN if httpclient is fixed by other clients. So the recommendation is to simply avoid UTF8 in headers, and encode using base64 any values going into http headers.
http://forums.asp.net/post/5219096.aspx
I have tried to repro this and as the user mentioned, this happens on selfhost but works fine on webhost.
Comments: As mentioned above, the issue here is that HttpClient does not understand UTF8 in headers. This is not part of the MVC/Web API project. And we did open a bug against HttpClient to allow for UTF8 as a fallback. However sending non ASCII characters in a header is going against the http spec, and is going to randomly break you EVEN if httpclient is fixed by other clients. So the recommendation is to simply avoid UTF8 in headers, and encode using base64 any values going into http headers.