vtk camera Pitch > 87 degree resets view-up

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Hi All,

I am using vtkCamea Pitch() for getting Coronal and Lateral view of a bone model.
But when I use Pitch value > 87 I get below warning.

vtkRenderer.cxx:1164 WARN| vtkOpenGLRenderer (00000291DB33D650): Resetting view-up since view plane normal is parallel

Below is the code snippet I use

femur_fig.camera.Roll(0)
femur_fig.camera.Pitch(90)
femur_fig.camera.Yaw(0)

Can somebody explain why vtkCamera behaves like this in case of Pitch()?
In CloudCompare I am able to get desired coronal and lateral view using 90 degree Pitch/Rotation