VTK warnings when modifying pipeline

Reported by Maik Beckmann:

This code

from enthought.mayavi import mlab


pts = mlab.points3d([0,1], [0,1], [0,1])

pts.mlab_source.set(x=[0,2])

works, but gives

ERROR: In /build/src/VTK/Filtering/vtkExecutive.cxx, line 756

vtkStreamingDemandDrivenPipeline (0x59b4900): Algorithm

vtkAssignAttribute(0x59bd8a0) returned failure for request:

vtkInformation (0x5ad6c60)

  Debug: Off

  Modified Time: 818743

  Reference Count: 1

  Registered Events: (none)

  Request: REQUEST_DATA_OBJECT

  ALGORITHM_AFTER_FORWARD:

where this is the emitting code in vtkExecutive.cxx in
vtkExecutive::CallAlgorithm(...)

   ...

  // If the algorithm failed report it now.

  if(!result)

    {

    vtkErrorMacro("Algorithm " << this->Algorithm->GetClassName()

                  << "(" << this->Algorithm

                  << ") returned failure for request: "

                  << *request);

    }

  ...

Though its reported as an error by vtk, it doesn't seem to break anything.