Weird zbuffer error on certain hardware

I have been writing an example app demonstrating opengl python and gtk,
however i have hit a weird issue you can see in the video below.

This only happens on one device i have tested another displays perfectly,
basically i am getting bleed through when rotating the objects and i am at
a loss as to why.

Any one able to help or suggest what might be causing this issue ?

http://youtu.be/74zD9wIodvQ

http://bazaar.launchpad.net/~oly/python-examples/trunk/view/head:/python-examples/gtk3/tut15/sample.py

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