Data set via SetPixelData / SetRBACharPixelData not shown

I’m trying to use a rubber band selection in one of my render windows.
However, while the selection itself works fine, something about this render window prevents the rubber band from being drawn; the selection works as normal, but during dragging, I see no rectangle being drawn.
So basically, the pixel data set via SetPixelData / SetRGBACharPixelData is not shown.

I’m using (an adapted version of) the vtkInteractorStyleRubberBand3D. I can reproduce a similar behavior in the example from
by setting DoubleBuffer on the render window to false (but I guess this is not exactly the same as this seems to disable updates on the window in a fashion so that it only updates when clicking inside the window; and when I check in my render window, double buffering is enabled.

I know this is kind of generic, but I’m hoping somebody can give me pointers towards other settings on the render window / renderer / … that might affect this? Or what kind of update call I might be missing?