[vtkusers] vtkAssembly acting strange?

[Chen, Elvis]

Greetings,

I am experiencing some strange behaviour using
vtkAssembly in that the rendition of vtkAssembly is
different than if I render each individual actor
separtely.  In my code, I have something to the effect
of (in Python2.2/VTK4):

t = vtkTransform()
t.SetMatrix([ <some rigid transformation> ] )

...
...
aActor.SetUserTransform( t )
bActor.SetUserTransform( t )
cActor = vtkActor # c doesn't use t

ren.AddActor( aActor )
ren.AddActor( bActor )
ren.AddActor( cActor )

This code would render what I expect.  However, if I
use vtkAssembly to render them:

t = vtkTransform()
t.SetMatrix([ <some rigid transformation> ] )

...
...
aActor.SetUserTransform( t )
bActor.SetUserTransform( t )
cActor = vtkActor # c doesn't use t

assembly = vtkAssembly()
assembly.AddPart( aActor )
assembly.AddPart( bActor )
assembly.AddPart( cActor )
ren.AddActor( assembly )

I would get a different visual effect than the 1st
code segment.  None of aActor/bActor/cActor are
displayed at the correct position/orientation.

Is there something obvious I'm missing?  

any help is very much appreciated,

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