The PTR download is not delivering you version 3.1. It's giving you the 3.0.8 PTR. So don't get it, there's really no reason to. You'll see all the bells and whistles go off here on WoW Insider when the download becomes available. We'll also get those coveted patch notes things up too.
Patch 3.1 Class Changes
All this information was recently posted on the EU PTR forums, so it looks like the PTR is getting closer and closer to release. Don't be surprised if it comes out today...Updated 9:18 a.m. EST
: Added "Patch 3.1 Class Changes" section.