Well this issue really hasn't been squashed yet.
I'm constantly having issues browsing in Yahoo's portal -
https://uk.yahoo.com/ - that I browse for news, etc.
I also get this issue in the avast forums.
1. Several time a day I have to disable https scanning and stop the web shield. I then try to refresh those tabs I can't view, but I'm still unable to view them.
2. Only when I enable https scanning and restart the web shield am I able to view the pages.
3. On occasion I also have to do this same exercise with the Mail Shield.
So there is certainly some work still to be done on HTTPS scanning for XP SP3.