Dear Mark, added the line with index_files_regexp to /etc/apt-cacher/conf.d/local.conf as a workaround and executed $ service apt-cacher restart
Then several $ apt-get update delivered error messages like W: The repository 'http://ftp.de.debian.org/debian testing Release' does not have a Release file. N: Data from such a repository can't be authenticated and is therefore potentially dangerous to use. N: See apt-secure(8) manpage for repository creation and user configuration details. After commenting out Acquire::http::proxy "http://mycomp:3142";; and removing all files from /var/lib/apt/lists apt-get update did its work as desired. After enabiling the proxy again in apt settings, apt-get update currently (now updates available) runs through without error messages. Please let me know if a fix is released, such that I can remove the teporary local.conf entry. Sorry for originally reporting twice in #821159 and #821155. Thanks for apt-cacher! Chris
