vtkOpenGLContextDevice3D & alpha blending

In vtk 8.2 I got alpha blending to work fairly easy in vtkPlotSurface by specifying 4 colorcomponents. This does not work anymore in trunk. It seems vtkOpenGLContextDevice3D never enables alpha blending.

These last 2 lines added to vtkOpenGLContextDevice3D::EnableDepthBuffer seem to be a "fix":

void vtkOpenGLContextDevice3D::EnableDepthBuffer()
{
  vtkOpenGLState* ostate = this->RenderWindow->GetState();
  ostate->vtkglEnable(GL_DEPTH_TEST);

  ostate->vtkglBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
  ostate->vtkglEnable(GL_BLEND);
}

I don't know if this is the proper solution (at the minimum it requires a separate function), but maybe someone who knows the code can have a look at this?

EDIT: this seems to only happen when using QVTKOpenGLNativeWidget