PDF/A export, different results (headless vs. GUI)

Exporting a document as PDF/A seams to work both ways
a) via GUI, with a warning about the transparency which is not allowed for PDF/A ==> perfect
b) command line, headless, no warning ==> the pdf will be created and is readable

But when checking the outputs from a) and b) above via the online check tool

document from a) passes the check, where doc from b) is invalid

  • The value for SelectPdfVersion is set to one in the registrymodifications.xcu file.
  • Using unoconv -f pdf -eSelectPdfVersion=1 etc. works, but is not really a beautiful solution in my context

Any hints?
Thank you.

I can’t figure out from your question does PDF after that unoconv command passes validation? Just as a reference: convert files to PDF/A on command line, headless mode [closed]; Unconv and LibreOffice at Ask Ubuntu

I’m on GNU/Linux with LibreOffice 5.1.5 installed in /opt/libreoffice5.1 and this command is working for me:

libreoffice5.1 --headless --convert-to pdf:writer_pdf_Export file.odt

And yes, you have to have ‘1’ in SelectPdfVersion in registrymodifications.xcu.

My test file passed validation.

See also Convert to command line parametar.