Tcp data received by server is duplicated in release mode (but not debug mode)

On Windows (XP) using Qt 4.5 with Visual Studio 2005, I'm implementing a simple Tcp server (using TcpServer) and client (using TcpSocket). It works fine in Debug mode, but in Release mode, the data received by the server is repeated, IE, when the client sends 'xyz' the server receives 'xyzxyz' via a single readAll(). Any tips? Is this a Qt issue, or some system socket issue? At the moment both the client and server are running on the same machine.

Do you have a very very minimal example code that reproduces this? I am 99% sure the error is in your code, as this sounds really strange and would have been discovered a lot earlier if it was in Qt.