When setting the environment of QProcess, a script without a shebang line fails to execute

How to reproduce:
1) Save the myprog perl script and test-env.cpp in the same directory.
2) Make executable myprog by "chmod 755 myprog".
3) Compile test-env.cpp without defining SETENV.
4) Launch the just compiled executable and verify that the the script is
actually executed.
5) Now compile test-env.cpp by using -DSETENV.
6) Launch again the executable and verify that it now fails to execute.