Missing prefix "navigation" in components.xml tree view

I am currently using JBoss Tools on the Seam perspective. I need to use several files for my navigation rules : pages.xml, section1.pages.xml, section2.pages.xml, ...

So, I open my components.xml file in "Source" view and add :
<navigation:pages>
<navigation:resources>
<value>/WEB-INF/navigation/pages.xml</value>
<value>/WEB-INF/navigation/section1.pages.xml</value>
<value>/WEB-INF/navigation/section2.pages.xml</value>
</navigation:resources>
</navigation:pages>

I also add in the "components" tag :
xmlns:navigation=http://jboss.com/products/seam/navigation
xsi:schemaLocation=http://jboss.com/products/seam/navigation
http://jboss.com/products/seam/navigation-2.2.xsd

And it works fine. But if I go to the "Tree" view of my components.xml, I have an error which tells me that the "navigation" prefix doesn't exist and that I have to remove it if I want to use the "Tree" view.