[abenedik]

When you show the bounding box, it is shown over your 3D model and this makes the mouse hit the bounding box instead of the model - this triggers the mouse leave event.

To prevent the bounding box from being hit by EventManager3D use the RegisterExcludedVisual3D method on EventManager3D and pass the Visual3D that is used to show the bounding box. This will remove it from being hit. When you hide the bounding box from the scene, call the RemoveExcludedVisual3D method so that it will not be checked again.