Python on Windows calling "make -j4" through a subprocess freezes, -j1 works

Question

When porting the build script to Windows, I noticed that I cannot call makewith the parallel build option -jfrom within python:

subprocess.call("make -j4 -f Makefile.win32 target".split())

This is on Windows 7 (in a virtual machine), with Python 3.4.2 (or 2.7.8), GNU Make 3.81 from MinGW. Make the call yourself cl.exeto compile about 40 C files. When you kill an insult make.exein Taskmanager, this is the result:

make: *** [target] Error 1
make: INTERNAL: Exiting with 1 jobserver tokens available; should be 4!