[xml] xml schema validation

["Kuperus, AgeJan" <AgeJan Kuperus wur nl>]

We recently upgraded from libxml2 2.6.7 to 2.6.17 and discovered that
the following xml, that was marked as valid in 2.6.7 is now marked as
invalid:

<wwwtest isn="103" xmlns="http://library.wur.nl/WebQuery/ns/wwwtest";
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance";
xsi:schemaLocation="http://library.wur.nl/WebQuery/ns/wwwtest
http://library.wur.nl/WebQuery/ns/wwwtest.xsd";>
        <elem>test</elem>
</wwwtest>

If we just create a prefix for it, it becomes valid again:

<x:wwwtest isn="103" xmlns:x="http://library.wur.nl/WebQuery/ns/wwwtest";
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance";
xsi:schemaLocation="http://library.wur.nl/WebQuery/ns/wwwtest
http://library.wur.nl/WebQuery/ns/wwwtest.xsd";>
        <elem>test</elem>
</x:wwwtest>

Can anybody tell me why the first form is invalid ?