Export fails when using SVG version 1.1 with unknown and not namespaced XML elements

All kinds of export will fail when an SVG image is included to the document. An error is displayd in the browser. You can make an example by exporting the following page as PDF or RTF:
https://studium.xarif.de/bin/Studium/Newton-Verfahren+zur+L%C3%B6sung+nichtlinearer+Gleichungen

Here is the same page but with png images: https://studium.xarif.de/bin/Studium/newton_export

The error message says something about invalid login data. But even if I am logged in as admin, the error occurs.