Permission problems with Roundcube Password plugin

Hi there,
Since moving to a new server, strangely something broke with the roundcube virtualmin password plugin.
I get the following error: ERROR CODE 2 - /usr/sbin/virtualmin must be run as root
However, the helper binary has the correct permissions (root:server-owner) and chmod 4550 as it did before.
If I su as the server owner and run the command in shell, it works fine. However it fails if php runs it.
PHP runs in CGI mode as the server owner user. I tested also creating a file from within the php script, and it creates a file owned by the server owner.
So I am quite puzzled right now as to why this doesn’t work anymore.
Any clues?

Whatever, I refactored the plugin and now it uses the remote API of Virtualmin. Should be slightly safer and less error prone.
I guess I will submit a patch to the roundcube devs.