The observed behavior is not a bug at all but a question of configuration. It is described in the apt-ftparchive man-page. Look for APT::FTPArchive::AlwaysStat.
If you want to check the modification dates of your archives simply
create a file
/etc/apt/apt.conf.d/99-ftparchive
with the following lines:
// Always check the modification time
APT::FTPArchive {
AlwaysStat "true";
};
Best regards
Heinrich Schuchardt
