The tag is present in Lintian version 2.104.318. That is the most recent version we know about.
The maintainer script apparently change a directory to a symlink not using dir_to_symlink command of dpkg-maintscript-helper, that take great care to avoid a lot of problems.
Please use the dpkg-maintscript-helper dir_to_symlink command.
Please refer to the dpkg-maintscript-helper(1) manual page for details.
This tag is experimental.