[vtkusers] VTK 7.0.0.RC1 (and releases before): X-OpenGL depth test(?) problems when using QVTKRenderWindow

[Sophonet]

Dear list,

when trying to run a Qt Python application using the 
qt.QTVTKRenderWindow, there are depth test problems.

Examples/Tutorial/Step1/Python/Cone.py works perfect, but with a simple 
QVTKRenderWindow example (based on 
https://gist.github.com/samueljohn/3090097, needs two more imports 
though), there are depth test problems, i.e. it appears that for some 
reason no depth test is applied (so the last drawn primitive is always 
visible on top).

When doing

export MESA_DEBUG=1

before running the two scripts, there is one warning in the 
Examples/Tutorial/Step1/Python/Cone.py,

Mesa warning: couldn't open libtxc_dxtn.so, software DXTn 
compression/decompression unavailable

[but everything looks fine],

but many more with the QVTKRenderWindow

Mesa: User error: GL_INVALID_OPERATION in glDrawBuffer(buffer=0x405)
Mesa: User error: GL_INVALID_OPERATION in glReadBuffer(buffer=0x405)
...

I am running Mesa 9.2.3 on my system (OpenSUSE 13.1), so I cannot switch 
to the OpenGL2 rendering backend (which might resolve the problem? - 
don't know...).

Any hints?

Thanks,

      sophonet