Sorry about the mess on the demo review -- since everybody gets write access to try things out, it tends to get messy over time. I just reset it now so it looks clean again, and should probably just stick the reset script in a cron job...
It's really odd that you got a nil default diff range. I can't reproduce it with either anonymous or authenticated access. If you can, could you please open an issue with more details so I can debug? Thanks!