Func_smokevolume issues - SDK2013

[Rhia]

Hey, I'm recently getting back into level design, and I'm trying to produce small smoke clouds to simulate dust or some sort of vapor emanating from grates in the floor, and func_smokevolume seems to be the right entity for the job, but in my experience so far, it appears to be a very finicky brush entity, and randomly not working at all.

In my situation, I have two groups of func_smokevolume entities. Both have the same exact settings and dimensions, they are simply in different positions. One group works fine, and while the other group seems to be rendering if I set mat_wireframe to 1, the particles are completely invisible. I've taken a series of screenshots to demonstrate what I'm seeing:

Grouping that works - normal view: http://i.imgur.com/ZpNKigs.jpg
Grouping that works - mat_wireframe 1: http://i.imgur.com/aLF5yEU.jpg
Grouping that doesn't work - normal view: http://i.imgur.com/BBFv6gr.jpg
Grouping that doesn't work - mat_wireframe 1: http://i.imgur.com/c7Lc0L6.jpg
Both groups in Hammer: http://i.imgur.com/SCdR6Ze.jpg

Does anyone have any clue what the problem is?