(Discovered by @Ryasmeen, I simplified the reproduction steps)
Steps to reproduce:
- Become a temporary user
- Visit Special:UserLogout
- Click "Submit"
The grey bar is still visible, although it should only appear while using a temporary account, and it shows the IP address as the "temporary username". I guess this is just a visual bug, but it could be disconcerting.
This is not reproducible when using the "Exit session" menu option with JS enabled, which logs you out in a different manner (unless you open that link in a new window to navigate to Special:UserLogout).