multi effect duration

[igroglaz]

        <item>
            <name>Potion Mage Bonus</name>
            <price>5000</price>
            <weight>3</weight>
            <effect>protectionFire=+50:duration 30,protectionWater=+50:duration 30,protectionAir=+50:duration 30,protectionEarth=+50:duration 30</effect>
        </item>

This potion works barely (to check as GM use: #create Potion Mage Bonus

it seems duration effect could be used only once for one effect. you can't have two durations in one effect