Memory leak when pos is changed

Hi!
I'm new to VPython project but I found a memory leak. There was something
mentioned about this problem before. I found it here:
http://sourceforge.net/mailarchive/forum.php?thread_name=AANLkTim8RL8kjW0%3DSK%2B9f-2A5TCQv6wAu9aTpBmisbNS%40mail.gmail.com&forum_name=visualpython-users.
But unfortunately I didn't find the solution.

I want to use VPython to render a surface which is beeing changed during the
program execution. To show you what I'm talking about I changed one of the
example programs (faces_heighfield.py). Now it looks something like this:

<code>

from visual import *

class Model:
    def __init__(self):
        self.frame = frame()
        self.model = faces(frame=self.frame, color=color.cyan)
        self.vertices = []

    def FacetedTriangle(self, v1, v2, v3, color=color.white):
        """Add a triangle to the model"""
        for v in (v1,v2,v3):
            self.vertices.append(v)

    def FacetedPolygon(self, *v):
        """Appends a planar polygon of any number of vertices to the
model"""
        for t in range(len(v)-2):
            self.FacetedTriangle( v[0], v[t+1], v[t+2] )

class Mesh (Model):
    def __init__(self):
        Model.__init__(self)

    def Draw(self, xvalues, yvalues, zvalues):
        points = zeros( xvalues.shape + (3,), float )
        points[...,0] = xvalues
        points[...,1] = yvalues
        points[...,2] = zvalues

        self.vertices = []

        for i in range(zvalues.shape[0]-1):
            for j in range(zvalues.shape[1]-1):
                self.FacetedPolygon( points[i,j], points[i,j+1],
                                                points[i+1,j+1],
points[i+1,j] )

        self.model.pos = self.vertices
        self.model.make_normals()
        self.model.smooth()
        self.model.make_twosided()

x = arange(-1,1,2./20)
y = arange(-1,1,2./20)

z = zeros( (len(x),len(y)), float )
x,y = x[:,None]+z, y+z

m = Mesh()

i = 0
dt = 0.1
while True:
    m.Draw( x, (sin(x*pi + i*dt)+sin(y*pi + i*dt))*0.2, y )
    i += 1
    rate(10)

</code>

When running this code we see quite a nice surface movement. That is what I
need. But the memory usage grows infinitely!
My question is... is there any  fix for this memory leak? Or do you know
other way to achieve similar visual effect in VPython?

I also tried to render the surface using convexes or points instead of faces
but the memory leak always existed...

Thanks in advance for your help.

Greetings,
Wojciech Frycz

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