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