[vtkusers] raycasting initially renders at low resolution

[The Merper]

Hi VTK-experts,
   I'm working on an app for viewing CT scans in 3D or 2D. When I initially
render the CT scan in 3D, the raycast rendering looks great (see the
attached normalResolution.png). However, when I switch from a 2D view
(performed via a vtkImageViewer2) back to the 3D raycast rendering, the
resolution is low (see the attached lowResolution.png). As soon as I
interact with the 3D rendering, the resolution returns to normal.
   Can anyone tell me how to fix this? I have AutoAdjustSampleDistance set
to "off" on the vtkFixedPointVolumeRayCastMapper that I'm using for the
raycasting. I would have thought that this would keep the resolution of the
raycasting constant.
    thank you in advance,
      -Merps
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