QNetworkAccessManager, "QObject::connect: Incompatible sender/receiver arguments..." warnings

I have multithreaded C++ application which uses QNetworkAccessManager in it's threads. Sometimes it gives me this warning message:

QObject::connect: Incompatible sender/receiver arguments
QNetworkSessionPrivateImpl::error(QNetworkSession::SessionError) --> QNetworkSession::error(QNetworkSession::SessionError)

Call stack looks like this:
QNetworkAccessManager::get ->
QNetworkAccessManager::createRequest ->
QNetworkAccessManagerPrivate::createSession ->
QSharedNetworkSessionManager::getSession ->
QNetworkSession::QNetworkSession ->
QObject::connect ->
QMessageLogger::warning

I tried to figure out what is going on. So I checked QObject::connect under debugger:

if (!QMetaObjectPrivate::checkConnectArgs(signalTypes.size(), signalTypes.constData(),
methodTypes.size(), methodTypes.constData())) {

signalTypes contains one item:
_type = 0 (int)
_name = "QNetworkSession::SessionError" (QByteArray)

methodTypes contains one item too:
_type = 1044 (int)
_name = "QNetworkSession::SessionError" (QByteArray)

QMetaObjectPrivate::checkConnectArgs checks types:

for (int i = 0; i < methodArgc; ++i) {
if (signalTypes[i] != methodTypes[i])
return false;

So I think this difference is the reason of the warning.

Another warning types I encountered are:

QObject::connect: Incompatible sender/receiver arguments
QNetworkSessionPrivateImpl::stateChanged(QNetworkSession::State) --> QNetworkSession::stateChanged(QNetworkSession::State)

QObject::connect: Incompatible sender/receiver arguments
QNetworkSessionPrivateImpl::usagePoliciesChanged(QNetworkSession::UsagePolicies) --> QNetworkSession::usagePoliciesChanged(QNetworkSession::UsagePolicies)