This behaviour is correct - queXML should not be filtered by relevance as it is supposed to be a paper based equivalent of the entire questionnaire.

I have 3 questions:

1) You say "This behaviour is correct - queXML should not be filtered by relevance" and therefore why the texts af the 2 buttons "PDF export" and "queXMLPDF export" are equivalent?
The first text is: "Export these responses as PDF", the second text is "Export these responses to QXML", and because of this, respondants understand the same responses.
The second text (for queXML) should be for example: "Export entire questionnaire including empty responses"

2) Why does the PDF export include also the equation questions? We have setted the flag "Always hide this question" to ON

3) why is the text formatting so different between PDF export and queXMLPDF export?
queXMLPDF export has a good formatting, but PDF export formatting is very very poor and page consuming

The pdf export can be changed with the new theme system.
It is rather time consuming and was made quickly, feel free to update it as you need it.

The QXML export is a machine readable export, that always represents the complete survey.
We will not change this export, since it was made for specific academic usage.
That is also why the button is called "<QXML>pdf export" because it should create a QXML formatted file.
Hence I wouldn't say that the buttons are equivalent.

That always hidden questions are shown is still a bug and will be fixed soon.

The button can be removed in the theme file, so if you don't want to show it, feel free to remove it.
If you like the QXML export please go for it, but we won't change it's behaviour.