The bug was todo with bpy.data and bpy.types becoming invalid, temporary fix is to re-assign them to the bpy module before running python operators or panels.
will look into a nicer way to get this working.
* Fix to make python panels callbacks get the actual
blender Panel as an argument, instead of any instance.
* Fix for callback validation in python 2.5, worked OK
in python 3.0 but gave error in 2.5 because it's a
method instead of a function there.
