It seems that the lighting performance update while is really great in game, has a major draw back in the editor.
If you have lighting quality on medium or low and add a static prop, then delete or change it's shadow mode, you'll see the prop's shadow remains until you force a new lighting calculation by hiding/un-hiding the light, or changing the light setting in the editor's properties.
Again, everything is working as expected, it's just odd to not have auto updating in the editor with static shadows. Maybe make it so that it uses the older update method if the engine is in the editor?