Spotlight and castShadows weird behavior

[ltcstar]

I run into a weird behavior regarding Spotlight and its castShadows field.

When castShadows is on, Spotlight sheds no light on objects if further (but still within radius). If castShadows is off, things return normal.

44 meters from ball's surface with castShadows on

the ball is glowing

45 meters from ball's surface with castShadows on

the ball is not glowing

45 meters from ball's surface with castShadows off

the ball returns to glow

Why is this happening?