Simple test program: (QTest)

QUdpSocket localsock1;
localsock1.bind(QHostAddress(QHostAddress::LocalHost));

QUdpSocket localsock2;
localsock2.bind(QHostAddress(QHostAddress::LocalHost));

QSignalSpy localsockspy(&localsock1,SIGNAL(readyRead()));

localsock2.writeDatagram("TestData", QHostAddress(QHostAddress::LocalHost), localsock1.localPort());
QTest::qWait(100);

QCOMPARE(localsockspy.count(), 1);

This will fail because readyRead was emit around 9 to 10 times. Older Qt versions (e.g. 5.2.1) does work correctly. This is not an actual bug, but the behaviour doesn't look right.