Qt crashes in qhttpsocketengine when using tcpsocket and proxy

I tried to open a tcp socket using a proxy.
But the Application chrashes in qhttpsocketengine.cpp on line 572:

char dummybuffer[4096];
while (d->pendingResponseData) {
int read = d->socket->read(dummybuffer, qMin(sizeof(dummybuffer), (size_t)d->pendingResponseData));
if (read >= 0) // maybe (read >= 0 && read < 4096)
dummybuffer[read] = 0; // <- chrash

because read returns a value of 4096 for me.