In the squid logs at /a/squid/archive/zero/zero.tsv.log-* on stat1002, we have zero markers for IPs that should not get one.
zgrep 198278752 /a/squid/archive/zero/zero.tsv.log-20130731.gz
The printed request holds a zero marker from Beeline Russia (zero=250-99), but the client IP is from Austria and not listed in Beeline Russia's IPs.
The request does not hold a Forwarded request.
The problem is not limited to Beeline Russia or Austrian IPs, as can be seen by running
zgrep 2215263992 /a/squid/archive/zero/zero.tsv.log-20130731.gz