rewrite.pl does not prevent cache miss

[John McCabe-Dansted]

Even though my rewrite.pl rewrites the URL to be the same, we still get a "miss" in the log.

For example, I have the following two TCP_MISSes my access.log

--
1485749121.397 128 192.168.1.152 TCP_MISS/200 109932 GET http://ftp.iinet.net.au/pub/ubuntu/pool/universe/l/leafpad/leafpad_0.8.18.1-4_amd64.deb - HIER_DIRECT/218.100.43.30 application/x-debian-package
1485749168.539 17 192.168.1.11 TCP_MISS/200 109932 GET http://au.archive.ubuntu.com/ubuntu/pool/universe/l/leafpad/leafpad_0.8.18.1-4_amd64.deb - HIER_DIRECT/218.100.43.30 application/x-debian-package
--

My rewrite.pl (attached) outputs the following to my rewrite.log, which seems to show that we have fetched exactly the same file twice:
--
http://ftp.iinet.net.au/pub/ubuntu/pool/universe/l/leafpad/leafpad_0.8.18.1-4_amd64.deb :: http://mirror.waia.asn.au/ubuntu/pool/universe/l/leafpad/leafpad_0.8.18.1-4_amd64.deb
http://au.archive.ubuntu.com/ubuntu/pool/universe/l/leafpad/leafpad_0.8.18.1-4_amd64.deb :: http://mirror.waia.asn.au/ubuntu//pool/universe/l/leafpad/leafpad_0.8.18.1-4_amd64.deb
--

I would expect the second access to be a hit since we are downloading the exact same file from the same URL.