I got this one too and honestly it's hilarious! I mean it's sad I don't get to pet more pups but I can just restart, so don't stress about it. First time nothing appeared, just doors, and second time there was a floor for a split second and then after that just doors.
FWIW I'm playing on a Mac, and it happened twice, once after 3 dogs and again after 5. I'd slap a dog image on the bottom of the Skybox, call this a "secret", and be done with it honestly :P.
Great, fabulous, and most excellent game BTW.