Adjusting the time and date is what it does whilst it starts up, but it should only last for a few seconds then return to normal time. You mean your time is not changing back even after some minutes?

Which Windows operating system version do you use?

If you are using Windows 7, try changing BearShare to Run in XP mode and run as administrator.

A clean install is where you uninstall the previous installation and remove all folders belonging to the program including the preferences folder.

I haven't run the BS Beta for ages.

But I just installed File_Girl's version & after a while (maybe 5 mins or so during which BS was adding files to my shared Library) found that I had an error from iTunes saying that time & date weren't set correctly.
That's never happened before when running the BS Beta. Never had a problem with time & date.

When I checked in Windows CP (XP) after maybe 10 minutes, the date was still set to 2005.

I've just used RevoUninstaller to remove BS & rebooted, so far all is back to normal.