Here's a little bug that happenned to me a bunch of times. I make some changes in the WebGUI (specifically, this happenned in the DHCP service settings and in the PPTP add user dialog), and press 'Save' (or whatever the button says).
Sometimes (pretty often) the interface just clears out to its default settings. It happens very fast, like its not talking to the server-side at all.
Clearing the cache fixes the problem for a while, then it happens again.
This problem was very obvious in IE 6.0.2800.1100 running on Windows 2000 server. I am able to reproduce it at will. (I access the WebGUI through HTTPS, although i dont think it matters).
The first times it happenned to me, I was sure the settings had actually been saved, so I think this could be a pretty dangerous problem under certain circumstances.