[abenedik]

I am glad that this is solved.

You may also subscribe to PreviewMouseDown, PreviewMouseUp, ... events in your Canvas and then set e.Handled (e is parameter to event  handler) to true in case the event was handled by your code and you do not want to pass it to the MouseCameraController.

If you would be using EventManager3D, you could also set the UsePreviewEvents to true on EventManager3D to allow having the same mouse buttons to have multiple "tasks".