[vtkusers] vtkScalarBarActor color changes

[David.Pont at ForestResearch.co.nz]

I am getting changes in coloration of my scalar bar. The colors initially
appear incorrect. If I zoom in on my main actor (so it is significantly
larger than the window) the scalar bar colours suddenly change to appear
correctly, but revert when I zoom back out.
At exactly the same zoom at which the colors change from incorrect to
correct a small actor (vtkPlaneSource, dimensions 1,1,0, origin 0,0,0)
appears.
Put another way: the actor is visible when the scalar bar colors are
correct; the actor is not visible when the colors are incorrect.
For the main actor dimensions are approx. 120,120,0 and origin 0,0,0
I am wondering if the fact that all actors have a z dimension of 0 has
something to do with it?
If I rotate the geometry the scalar bar colors flicker and change
intermittently!

I have tried calling vtkRenderer->ResetCameraClippingRange but this had no
effect.

I have run out of ideas... by the way I am still working with vtkVersion
3.1.0
I am actually using a texture applied to the main actor, which might have
something to do with it (i have not had this problem when I do not use
texture).
My current guess is something happening during rendering (a conflict around
actor bounds, clipping, polygon shading, texturing...).

   can anyone shed any light on this ?
   Dave Pont