Hi @ll
I have tested i little bit more. After activating RoundcubePlugins, it is required to restart imscp_panel. A full rerun of installer is not required.
Deactivating is no problem. The Plugins are removed from webmail.
So, I looked at imscp_panel. It uses the php.ini in /var/www/fcgi/master/php5/. There I disabled soap-cache, opcache and apc. After restarting imscp_panel, I can activate/deactivate RoundcubePlugins and the changes are effecting immediately.
I hope this help.
Greets
Chris