apt-mirror is not able to handle URLs with embedded port numbers

When trying to run apt-mirror against approxy on port 9999 apt-mirror crashes with:

Proceed indexes: [Psh: cannot open debian-hm/ubuntu//dists/natty/main/binary-amd64/Packages.gz: No such file
apt-mirror: can't open index in proceed_index_gz at /usr/bin/apt-mirror line 451.

The index file Packages.gz exists in
/var/spool/apt-mirror/skel/debian-hm:9999/ubuntu/dists/natty/main/binary-amd64/Packages.gz

ProblemType: Bug
DistroRelease: Ubuntu 11.10
Package: apt-mirror 0.4.8-3ubuntu1
ProcVersionSignature: Ubuntu 3.0.0-14.23-generic 3.0.9
Uname: Linux 3.0.0-14-generic x86_64
ApportVersion: 1.23-0ubuntu4
Architecture: amd64
Date: Wed Jan 25 13:37:20 2012
PackageArchitecture: all
ProcEnviron:
 PATH=(custom, no user)
 LANG=de_DE.UTF-8
 SHELL=/bin/bash
SourcePackage: apt-mirror
UpgradeStatus: No upgrade log present (probably fresh install)
mtime.conffile..etc.apt.mirror.list: 2012-01-25T13:26:12.346087