We run approximately 50 virtual machines off thin clients in a windows 2008 server environment with users running Windows XP. Several weeks ago, I was experimenting with adding several sites to the bypass proxy server list in a gpo that is linked to the virtual machines OU that provides users with the proxy settings.
When i was finished adding and removing some sites, everything worked fine until a couple of days later when the wrong addresses began appearing in users 'bypass proxy server for local addresses' exceptions list causing them not to be able to reach these sites.
There is no trace of these sites in any group policy, however, it appears that it saves the incorrect settings back to ntuser.dat at the end of the day (they are using roaming profiles) even though the correct settings were in place before logging out.
We have attempted to resolve the problem by using logon scripts, registry keys through gpo's and recreating the original gpo's and overriding gpo's however the problem still occurs.