(I've done the usual rm /var/lib/apt/lists/* ; service squid-deb-proxy stop ; rm -rf /var/cache/squid-deb-proxy/* ; service squid-deb-proxy start and re-tested with similar results.)
(I've done the usual rm /var/lib/ apt/lists/ * ; service squid-deb-proxy stop ; rm -rf /var/cache/ squid-deb- proxy/* ; service squid-deb-proxy start and re-tested with similar results.)