[RCD] Malfunctioning quota hook?

I'm unsure if it's a bug in roundcube or if I'm doing it wrong so I'm posting on the list instead of making a ticket in the trac system.

Anyhow, I'm trying to add local directories of my users so that the size of their other personal directories are added to the total used quota. The problem is that the quota bar isn't affected by my changes. Here's some code for reproduction:

    public function quota($args) {
            $args['used'] .= 1048576;
            return($args);
    }

The quota is completely unaffected by this, judging from the quota bar that works in other cases.

Is this a bug or am I doing it wrong?

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