Can't build Debian packages from the generic .tar.gz sources file, its debian/ directory seems incomplete

I wanted to have the sources and especially the debian/ directory from the 5.5.25 release so i could try to create Debian packages for TokuDB (latest version is based on MariaDB 5.5.25 which is not the latest release as of now) but there is only the latest release source package available on the Debian/Ubuntu repositories, so i tried to use the "mariadb-5.5.25.tar.gz" non distro-specific sources that includes the "debian/" directory normally used for Debian/Ubuntu packages creation.

Unfortunately, if you try to do a dpkg-buildpackage from these sources, you will hit errors telling you that mandatory files are missing from the "debian/" directory :

[...]
dpkg-buildpackage: host architecture amd64
dpkg-buildpackage: warning: debian/rules is not executable: fixing that.
dpkg-source --before-build mariadb-5.5.28a
dpkg-source: error: cannot read mariadb-5.5.28a/debian/control: No such file or directory
dpkg-buildpackage: error: dpkg-source --before-build mariadb-5.5.28a gave error exit status 2

The debian/ directory size is bit smaller on the tarball version than the repository one and some files are missing :

$ du -s mariadb-5.5-5.5.28-mariadb/debian/ mariadb-5.5.28a/debian/
1392 mariadb-5.5.28a/debian/
1448 mariadb-5.5-5.5.28-mariadb/debian/

Is this an expected behavior (in that case, where could i retreive a working debian/ directory from a previous release) or a bug?

ps: same problem happens on 5.5.28a and 5.5.25.