Why does grouping change the shader reaction?

I have two objects. They both came from 3dsmax, and are basic boxes. When I apply a basic diffuse shader, one colors correctly and the other becomes a darker matte color. They're both on the default later, they both receive and cast shadows.

Here's what I'm curious about: the one that colors correctly is a single mesh that was 'grouped' to itself in max. The other wasn't. When I added a group to the incorrectly colored boxand re-export, it worked fine. Anyone have a clue as to why this happens?