How are particle emitters affected by objects behind? I am attempting to build a light beam and so far it works as long as there is no objects behind. Once it steps over an object that is behind, the intensity seems to diminish its power depending on the qualities of the material behind.

I would like this not to happen, as I need a homogeneous streak. How could elements be influencing this scene and how could I change it?

Blender file: http://we.tl/H7hwWtIqLL

A visual example:
The problem is caused by the transparent material of the blue 'Cylinder'.
You can fix this by going to its material and then under the Transparency tab and setting your transparency method from 'Z Transparency' to 'Raytrace'.
This should fix your problem!