To confirm teed’s issue, I am experiencing the same problem with a CPU based particle system that is placed in the level as an actor (I have also attached it via a component in my character blueprint). You can see clearly see collisions live in the editor, but once in game, the collisions are passing right through the objects that have the assigned collision type.
In my example, I set the Collision Completion Option to Freeze Translation.
I have also added all possible Collision types (world static/dynamic, pawn etc) to see if it was a problem with a certain type of actor collision setting. In the editor, the collisions occur and the particles are accumulating from their collisions with the terrain. Though, after entering game to test it out, the particles do not react as they do in the editor.
I am experiencing this in 4.6.1. Also to note, level blueprints are not used in my test.