Packages.gz not found because instead searching for Packages only

apt-get update gives a warning (not only apt-get: synaptic or all other packet managing tools too):

W: Failed to fetch http://de.archive.ubuntu.com/ubuntu/dists/precise/multiverse/binary-amd64/Packages 404 Not Found [IP: 141.30.13.20 80]

This warning is ok, since "Packages" doesn't exist at "http://de.archive.ubuntu.com/ubuntu/dists/precise/multiverse/binary-amd64/". "Packages.gz" (or Packages.bz2) do exist indeed. Two possibilities:

1. The string "http://de.archive.ubuntu.com/ubuntu/dists/precise/multiverse/binary-amd64/Packages.gz" is exactly 3 characters to long for the defined buffer, thus shortened by ".gz".
2. The Repository isn't correctly initialized, stating "Packages" instead of "Packages.gz" or "Packages.bz2" to load.

Since all other repositories are loaded and look the same (and defining a new repository holding the very same files than this ony, but with a shorter path makes it load) I am tending to the first possibility ...

ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: apt 0.8.16~exp12ubuntu10.2
Uname: Linux 3.4.6 x86_64
ApportVersion: 2.0.1-0ubuntu11
Architecture: amd64
Date: Mon Jul 23 09:56:45 2012
InstallationMedia: Xubuntu 11.10 "Oneiric Ocelot" - Release amd64 (20111012)
ProcEnviron:
 LANGUAGE=de_DE:en
 TERM=screen-bce
 PATH=(custom, no user)
 LANG=de_DE.UTF-8
 SHELL=/bin/bash
SourcePackage: apt
UpgradeStatus: Upgraded to precise on 2012-07-16 (6 days ago)