HelixViewport3D on docking pane, model zooms out

In my app, I add various Helix 3d objects (RectangleVisual3D, PipeVisual3D, etc) to the HelixViewPort3D via viewPort3D.Children.Add(new RectangleVisual3D), etc.

The HelixViewPort3D is hosted in an content Pane of a TabGroup of a docking control. When I click on other tabs, then click back on the tab that contains the viewport, the "model" zooms out (smaller), and continues to do so each time I click another tab then click back.

Any idea as to what this issue could be?

Is ZoomExtentsWhenLoaded set to true in the HelixViewport3D? The control is probably unloaded when changing tabs...