When I do a soft proof in Photoshop with a printer profile for a matte paper, I get a different look in the shadows if I use Gamut Warning or not. It's not that I get a Gamut Warning, it's a change in the smoothness of the shadows. The first image is with soft proofing and gamut warning activated, the second is with soft proofing activated but with gamut warning deactivated.
I've never seen an image change if I activate or deactivate gamut warning. A bug in the profile or a bug in Photoshop? I use CC2014.