On my server "broek", the Owncloud web interface wasn't working. As it turned out, each request to a PHP page returned a file for download instead of serving the PHP page.
Based on this thread I tried
dpkg -l | grep libapache and saw libapache-mod installed, but httpd.conf was empty.
So I resorted to removing PHP altogether:
sudo apt-get remove php5
Unfortunately this uninstalled Owncloud too.
And reinstalled PHP:
sudo apt-get install php5 sudo apt-get install libapache2-mod-php5
After restarting apache server, serving PHP files worked again. So I tried reinstalling Owncloud:
sudo apt-get install owncloud
The Owncloud web interface then worked again and even remembered the configuration!