QAuthenticator hard-coded to HTTP in SPNEGO/Negotiate

I am connecting to a Windows Communication Foundation (WCF) web service, using QNetworkRequest.  I have a slot for QNetworkAccessManage::authenticationRequired, and am supplying credentials using the QAuthenticator in that slot.  Server replies back with HTTP 401 Unauthorized.  Also the HTTP headers from the server include "WWW-Authentication: Negotiate".  This is on a Windows client also, and uses the SSPI library (not GSSAPI).

qauthenticator.cpp, around line 1631 looks like this:

// Calculate target (SPN for Negotiate, empty for NTLM)
std::wstring targetNameW = (
        method == QAuthenticatorPrivate::Negotiate
        ? QLatin1String("HTTP/") + host
        : QString()
    ).toStdWString();

The code then flows into a call to InitializeSecurityContext() and passes the targetNameW from above as a parameter.  The function call fails with SEC_E_WRONG_PRINCIPAL.  If I change the targetNameW to instead use QLatin1String("SPN/") + host, the call to InitializeSecurityContext() succeeds and the web service call works as expected.