Lighting not previewing in 4.3 but did in 4.2.1

As you can see in this video posted by Unreal; - YouTube
any new items placed into the map automatically have a rough shadow below them that updates automatically.

This may be due to my own fault but since I began working in 4.3 items no longer have any shadow at all when I spawn them in apart from some lighting on their own faces, infact, adding a new cube to a map that already has the shadows built will remove all shadows from the map until I build them all again, please can somebody tell me why I no longer have automatic shadows in the editor and how to get them back?