I knew it. I absolutely did that a million times but nothing happened.
I suspected it might be the sequence I was doing, and turned out I was right. If I went to the mirror cabinet the first thing, it would trigger the search dialog with Nevin just fine.
Actually, once you started with the mirror cabinet, then the rest of the stuff on the 2nd floor, Nevin will ask you to go to the rented space. You don't even need to examine anything downstairs. But for some reason, if I examined some other stuff first, the cabinet will be inaccessible.
Anyway, I can continue with the story now. Thank you for the pointer.