Curious shadow bug using point lights [video]

Hi guys!

While testing the point lights with standard geometry recently I noticed the following strange bug; when changing the elevation and angle of the camera while looking at a point light inside an exploded cube, the shadows of the back faces stop displaying at certain angles.

Here is a video of the effect:

http://www.youtube.com/watch?v=kIjZoDWmjGQ&feature=youtu.be

Does anybody know why this could be occurring? The camera is set to deferred rendering, all the sides have a standard shader and are set to cast shadows and the light itself is a point light with normal settings.