I tried this both on your demo site (1.8.0 alpha 0), and on my work install of 126.96.36.199.
I see that the demo instance shows the problem here:
The "power" icon appears to be loaded from
... however, my work instance does not use gravatars, and if someone has a browser plugin that blocks certain kinds of cross-site requests (see RequestPolicy), then no icon shows here.
Is there any way that this icon can be defaulted to something actually installed on the reviewboard server, instead of being loaded from a remote site?