[xsl] xmlns in the root element prevents transformation

["Manuel Souto Pico terminolator@xxxxxxxxx" <xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx>]

Dear all,

This transformation gives me an empty output file:
https://xsltfiddle.liberty-development.net/gVhEaiQ

However, if I remove the xmlns="urn:oasis:names:tc:xliff:document:1.2 bit
from the XLIFF root node, then it works.

Could somebody help me understand why that happens?

Thanks in advance.

Cheers, Manuel