Comment 1 for bug 1156996

I am able to reproduce the issue on debian 7 with Percona Server 5.1/5.5/5.6. Installed PS packages from percona repo and during upgrade i found links are re-created.

# apt-get install percona-server-server-5.5 percona-server-client-5.5 percona-server-common-5.5

* Verified from rc.d scripts and found mysql is added once i installed PS 5.5 from Percona repository.
# ls -la /etc/rc* | grep mysql
lrwxrwxrwx 1 root root 15 Dec 24 06:18 K02mysql -> ../init.d/mysql
lrwxrwxrwx 1 root root 15 Dec 24 06:18 K02mysql -> ../init.d/mysql
lrwxrwxrwx 1 root root 15 Dec 24 06:18 S17mysql -> ../init.d/mysql
lrwxrwxrwx 1 root root 15 Dec 24 06:18 S17mysql -> ../init.d/mysql
lrwxrwxrwx 1 root root 15 Dec 24 06:18 S17mysql -> ../init.d/mysql
lrwxrwxrwx 1 root root 15 Dec 24 06:18 S17mysql -> ../init.d/mysql
lrwxrwxrwx 1 root root 15 Dec 24 06:18 K02mysql -> ../init.d/mysql

* Removed mysql service from rc.d directory to prevent auto-start of mysql service on OS reboot.
# update-rc.d -f mysql remove
update-rc.d: using dependency based boot sequencing

# ls -la /etc/rc* | grep mysql

Upgraded to Percona Server 5.6 and found links are re-created.

* Removed PS 5.5 packages.
# apt-get --purge remove percona-server-server-5.5 percona-server-client-5.5 percona-server-common-5.5

* Started upgrade to PS 5.6
# apt-get install percona-server-server-5.6 percona-server-common-5.6 percona-server-client-5.6

# ls -la /etc/rc* | grep mysql
lrwxrwxrwx 1 root root 15 Dec 24 06:35 K02mysql -> ../init.d/mysql
lrwxrwxrwx 1 root root 15 Dec 24 06:35 K02mysql -> ../init.d/mysql
lrwxrwxrwx 1 root root 15 Dec 24 06:35 S17mysql -> ../init.d/mysql
lrwxrwxrwx 1 root root 15 Dec 24 06:35 S17mysql -> ../init.d/mysql
lrwxrwxrwx 1 root root 15 Dec 24 06:35 S17mysql -> ../init.d/mysql
lrwxrwxrwx 1 root root 15 Dec 24 06:35 S17mysql -> ../init.d/mysql
lrwxrwxrwx 1 root root 15 Dec 24 06:35 K02mysql -> ../init.d/mysql

So, mysql daemon script added after upgrade implicitly to rc.d directory.