
So, I've tried everything I can think of on this one...
As you can see in the image the monkey head is close behind the smoke, and the transparent cubes are slightly in front of the smoke.
This is in BI, and the smoke and cubes are both ray-traced. The monkey is just a plain solid colour.
I did notice that only the closer parts of the monkey show through the smoke behind the cubes, and it works perfectly well for the more distant parts.
Also, here's a .blend file.
Thanks!
UPDATE:
Aside from taking the cubes out of the smoke, moving the background object out of the domain also works...
Outside domain,

Inside domain,

Thanks for the help gandalf3. If anyone can figure it out based on this info. that would be much appreciated. And yes, if it is a bug, is there a way to address this issue?
Many thanks!