conflict between fortran+iso_c_binding (via ctypes or cython) and matplotlib when reading namelist

lib.f90

module mylib

  use iso_c_binding, only: c_double

  implicit none

  double precision :: g

  contains

    subroutine read_par() bind(c, name="read_par")
      namelist /block/ g
      open(8, file='namelist.nml')
      read(8, nml=block)
      close(8)
    end subroutine

    subroutine print_par() bind(c, name="print_par")
      print*, 'g', g
    end subroutine

    subroutine set_par(x) bind(c, name="set_par")
      real(c_double), intent(in), value :: x
      g = x
    end subroutine

end module

lib.pyx

cdef extern:
    void read_par()
    void print_par()
    void set_par(double *g)

def read_par2():
    read_par()

def print_par2():
    print_par()

def set_par2(double g):
    set_par(&g)

makefile

PYDIR=$(HOME)/anaconda/include/python2.7

ctypes:
	gfortran --shared lib.f90 -o lib.so -fPIC

cython: 
	gfortran -c lib.f90 -o lib.so -fPIC
	cython -a lib.pyx
	gcc -shared lib.f90 -pthread -fPIC -fwrapv -O2 -Wall -fno-strict-aliasing -I$(PYDIR) -o lib.so lib.c -lgfortran

clean:
	rm -rf build *.mod *.so *.o *.c *.html

namelist.nml

&block
    g = 9.81
/

test_ctypes.py

from ctypes import CDLL, c_double
import matplotlib.pyplot as plt

f = CDLL('./lib.so')

print "Read param and print to screen"
f.read_par()
f.print_par()

# calling matplotlib's plot command seem to prevent
# subsequent namelist reading
print "Call matplotlib.pyplot's plot"
plt.plot([1,2],[3,4])

print "Print param just to be sure: everything is fine"
f.print_par()

print "But any new read will lose decimals on the way!"
f.read_par()
f.print_par()

print "Directly set parameter works fine"
f.set_par(c_double(9.81))
f.print_par()

print "But reading from namelist really does not work anymore"
f.read_par()
f.print_par()

test_cython.py

import matplotlib.pyplot as plt
from lib import read_par2 as read_par, print_par2 as print_par, set_par2 as set_par

print "Read param and print to screen"
read_par()
print_par()

# calling matplotlib's plot command seem to prevent
# subsequent namelist reading
print "Call matplotlib.pyplot's plot"
plt.plot([1,2],[3,4])

print "Print param just to be sure: everything is fine"
print_par()

print "But any new read will lose decimals on the way!"
read_par()
print_par()

print "Directly set parameter works fine"
set_par(9.81)
print_par()

print "But reading from namelist really does not work anymore"
read_par()
print_par()

See question here:
http://stackoverflow.com/questions/28915761/conflict-between-fortraniso-c-binding-via-ctypes-or-cython-and-matplotlib-whe