Hi. I tried to figure out what's going on.
On a system where it fails: dpkg-buildpackage -> fails find . -type d | xargs chmod g-w dpkg-buildpackage -> this time it works Looks like some check should be relaxed. In Debian, the default umask changed in trixie, so it is certainly a problem that a simple dpkg-buildpackage is unable to build the package. Thanks.
