Interacting with slices in layered Renderers

Hi everyone,

my project is using a vtkImageViewer2 with two renderers used to display volume slices.
One renderer has a blend of ImageData (PET scans), the other one is used to superimpose segmentated parts (vtkActors) (tumors) to the image.

The idea is to display slices of the volumes, whilst the segmentations are superimposed to the PET image so that we can interact with them. Showing the slices seems to be alright. The problem arises when I zoom (vtkInteractorStyleImage) into the window, because then all of the actors in the upper renderer are displayed as 3D volumes superimposed to the current slice. If I change the slice then both volumes are correctly sliced and displayed, until I zoom in/out again.

This happens regardless of which Renderer the InteractoryStyle is connected to.

After changing slice (displaying correctly):

After zooming in (full volume over slice).

I would like to keep the zooming function, so changing to e.g. vtkInteractorStyleRubberBand2D won’t be a viable solution afaic.
As you may also see, the segmentated volume/slice has a distance to the image in the other renderer that is evident when moving the camera around. How can I have both volumes be “on the same plane”?

Should I extend the InteractoryStyle to call the slicing function after zooming in/out, or is there a better solution than this?

Any advice is greatly appreciated.
Thanks in advance, Valentin