localhost connections showing source address 0.0.0.0

[Kris Kennaway]

Going back at least as far as January 2007 some of the package build 
machines have occasionally experienced a problem where a fetch(1) via a 
localhost:3128 squid proxy are denied because squid sees the connection 
as having a source address of 0.0.0.0 instead of 127.0.0.1.  I thought 
this had stopped but it turns out it was just masked by all the other 
TCP issues and was still persisting at a low rate (only ~300 occurrences 
on the machine I checked since January).

Can anyone work out how this is happening, or give suggestions on how to 
debug this further?

Kris