Create a basic executable with system("pause") function or getchar() function.
This is the code (same than exeTest.exe in attached file):
#include <iostream>
#include <Windows.h>

int main (int argc, char* argv[])
{
system("pause");
return 0;
}

Code to test the bug:
QProcess *test = new QProcess();
test->start("exeTest.exe");
test->waitForStarted(1000);

test->close(); // exeTest is closed in task but we never quit close() function. It happens also if we try to delete pointer without calling close() function
delete test;

I didn't have this problem with previous version of Qt (4.7.4) but I have it with Qt5 (I tried with Qt 5.0.2 and 5.1.0)