Maybe you are on some system that has to authenticate somewhere to get you on the internet? Some network servers will reject you if you're computer doesn't have the right time.
You've got a work around it sounds like, but you should be able to fix it here.
If you're using XP...
XP Daylight Savings Time Patch
If you're using Vista or something, then you can find other versions a few paragraphs down this page:
Windows DST Article
Should be easy to just run the patch and straighten it out. Hope that helps.