If you apt-get install phpmyadmin on Debian/Ubuntu, you will notice the quoted warning message:
Server running with Suhosin. Please refer to documentation for possible issues.
You will get reference and possibile solutions here.
A fast get to achieve a fully working phpmyadmin on a trusted environment, is to enable the simulation mode on the phpmyadmin vhost, editing /etc/apache2/conf.d/phpmyadmin.conf and adding:
php_flag suhosin.simulation On
inside the relevant IfModule directive, for example [IfModule mod_php5.c] if you are using libapache2-mod-php5.