apt does not update directory permissions

[Christoph Mathys]

We are using debian packages to distribute our software inside the
company. Recently I messed up the permissions inside a package: A
whole directory-tree suddenly belonged to root:root, when it should
belong to someone else. The fix for the package was quick, permissions
now look ok again (checking with dpkg -c and clean install). However,
when I update the old (broken) package (dpkg -i or apt-get install,
does not matter), only the file permissions get corrected, all folders
still have wrong permissions.

Is this a "feature" of apt to only correct file permissions? Do I
seriously need to hack something into postinst to fix this correctly?

Christoph