Why isn't the cube's collision properties working? You can see the particles in the above image, but, despite the cube having had "collision" properties in the settings, it won't block the particles?



...and here's the physics settings I'm using.


Here is the .blend file: https://drive.google.com/file/d/0ByScwSCTIaUGUkZoTXhoTFhjU3c/edit?usp=sharing
Many thanks
This reproducable as Phillip Kinkade mentioned, when the particle system animation was baked without the collision object, later adding wouldn't make them collide. 


Free Bake
Position your collision object
Bake




After the three steps above no more particles will go through the cube: