Using Kolab_Development packages under CentOS 7, the web client throws fatal errors when opening the calendar because Sabre/VObject classes are not found. It appears that the Composer autoloader is not built correctly during packaging. Similar to iRony or other projects, a stub composer.json file with path definitions to /usr/share/... should be used for building:

{
    "name": "kolab/roundcubemail",
    "description": "Roundcube Webmail for Kolab",
    "license": "GPL-3.0",
    "require": {
	"php": ">=5.3.3"
	},
    "autoload": {
	"psr-0": {
	    "": "/usr/share/pear/"
	    },
	"psr-4": {
	    "": "/usr/share/php/"
	    }
	}
}