Forgive me - but from this thread I got the impression that you're suggesting that it's actually a problem in avast. Let me say that this is definitely not the case here.
An inability to correctly work with local proxies is a long-standing issue in Sygate. You may try to find more info about this problem on a number of websites and forums.
There has also been some discussion about this on the official avast support forum. Please see e.g.
http://forum.avast.com/index.php?topic=11332.0
Anyway, thanks for the heads up.
Cheers
Vlk