Reg[Qt4-5]:Windows: QProcess::WaitForFinished() takes way longer

QProcess WaitforFinished() takes at least 5 times more time than Qt4 on windows.
Attached example reproduces this:

In the example The main program launches a sub process, waits for this process to finish and read all its output (for timings purposes, this is done 500 times)
the child program simply outputs some data on stdout and exits (135KB of
data are written)