[vtkusers] volume rendering and interactor style (bug?)

[Shang Mu]

I'm volume rendering something using vtkOpenGLVolumeTextureMapper3D,
and the window is a vtkRenderWindowInteractor. When I used camera
mode, the interactor worked fine (generally smooth with a little lag),
but when I switch to actor mode and move the actor, it takes more than
half a minute to render a scene.

Anyone else experienced similar case? Is it a bug or something? I'm
using wxPython under Windows.