addMagicPercent Help. Doesnt work on devlands 8.1 xml

[Big M O O K]

In evolutions servers they have this, but not in devlands 8.1 xml but thats what i use.

I want blue robe to use this but the attribute addMagicPercent dont work :\ Can anyone help me make this work?

<item id="2656" article="a" name="blue robe">
<attribute key="description" value="It is a magic robe."/>
<attribute key="weight" value="2200"/>
<attribute key="armor" value="11"/>
<attribute key="slotType" value="body"/>
<attribute key="addMagicPercent" value="15"/>
</item>