[Matplotlib-users] Memory usage

Hello to all,

This is yet another question about matplotlib not freeing memory, when closing a figure (using close()).
Here is what I'm doing (tried with several backends, on MacOSX and Linux, with similar results):
--------------------
import matplotlib as mpl
from matplotlib import pylot as plt
import numpy as np

a = np.arange(1000000)
mpl.cbook.report_memory()
# -> output: 54256
plt.plot(a)
mpl.cbook.report_memory()
# -> output: 139968
plt.close()
mpl.cbook.report_memory()
# -> output: 138748
--------------------

Shouldn't plt.close() close the figure _and_ free the memory used by it?
What am I doing wrong ?
I tried several other ways to free the memory, such as f = figure(); ... ; del f, without luck.

Any help appreciated !

P.S. : side question : how come the call to plot take so much memory (90MB for a 8MB array ?). I have read somewhere that each point is coded on three RGB floats, but it only means an approx. 12MB plot... (plus small overhead)

Jules