Creating vhost breaks phpmyadmin

Wired problem I never faced before in the many years I use virtualmin:

• I set up a fresh VE w. a basic debian 7, updated, upgraded to the latest (stable) version (I used a proxmox template, that successfully deployed many other VEs w. virtualmin and phpmyadmin)
• installed virtualmin using install.sh
• installed phpmyadmin using apt-get
• http://hostname.tld/phpmyadmin works
• I create the 1st vhost through virtualmin
• http://hostname.tld/phpmyadmin is broken - it downloads the raw source of php file - php is no longer parsed. Same for http://[IPv4]/phpmyadmin and http://[domain of newly created vhost]/phpmyadmin
• I remove the vhost through virtualmin
• http://hostname.tld/phpmyadmin works again
  

As I deleted and re-built this VE for the 3rd time now and the problem reproduces, I thought I'd post here and ask for ideas, proposals, solutions - many thanks in advance! :)