Jagged edges on hidden geometry

[sabelli.a]

Hi to all, I was just testing the FumeFX demo and while playing around with it I noticed that when smoke hits an object or the source is a geometry the render comes out with jagged edges, I'm using scanline, I tried many different settings, scene scale, lower voxel grid and other parameters but nothing changes, maybe it's a demo restriction or something, any hint is appreciated.

Here's an image of what I'm talking about.

Thanks