Why is there so much outdated font info in my PDF (XML) metadata?

Question

I am creating a PFD/A compliant file. I finally managed to set pdfcreator, pdfproducer and all other fields to my liking (using hyperref and hyperxmp) and even suppress PTEX.* info. All is good.

Except: Checking the file's XMP data, under the namespace http://ns.adobe.com/xap/1.0/t/pg, there is xapTPg:Fonts, “an unordered array of fonts that are used in the document (including any in contained documents)” according to the docs. Where does this come from? It contains all the fonts I might have used at some point, starting with Computer Modern, but there's no trace of them left anywhere in my source files. Deleting all auxiliary files did not help.

I am using LuaLaTeX to compile the .pdf.

ETA: Ok, so here's the MWE. I am using the freely available IBM Plex fonts, and this color profile.

% !TeX program  = lualatex
% !TeX encoding = UTF-8 Unicode

\documentclass[fontsize=11pt,twoside]{scrreprt}

\usepackage{fontspec}
    \setmainfont[BoldFont={IBMPlexSerif-SemiBold.ttf}]{IBMPlexSerif-Regular.ttf}
    \setsansfont[BoldFont={IBMPlexSans-Medium.ttf}]{IBMPlexSans-Regular.ttf}

\usepackage[ngerman]{babel}
\usepackage{hyperxmp}

\usepackage[pdfa]{hyperref}

    \immediate\pdfobj stream attr{/N 3}  file{eciRGB_v2.icc}
    \pdfcatalog{%
        /OutputIntents [ <<
            /Type /OutputIntent
            /S/GTS_PDFA1
            /DestOutputProfile \the\pdflastobj\space 0 R
            /OutputConditionIdentifier (eciRGB v2)
            /Info(eciRGB v2)
        >> ]
    }

\hypersetup{pdftitle={My Title},pdfauthor={Ingmar},pdfproducer={},
pdfcreator={},pdfaconformance={U},pdfapart={2},keeppdfinfo}

\pdfvariable suppressoptionalinfo 15
\pdfvariable omitcidset=1

\begin{document}

\chapter{Problemaufriss}

Nicht als öffentliche Sachen sind dagegen Sachen zu verstehen, die bloß mit einer 
Legalservitut belastet sind, wie dies zB beim Betreten des Waldes als 
Duldungspflicht des Waldeigentümers (§ 33 Abs 1 ForstG), bei der sog 
„Wegefreiheit im Bergland“ (zB § 1 Abs 1 sbg WegefreiheitsG, § 47 Abs 1 oö 
TourismusG), bei der luftfahrtrechtlichen Überflugsbefugnis (§ 2 LFG) oder auch 
bei speziellen Duldungspflichten (zB § 72 WRG) der Fall 
ist.\!\footnote{\textsc{Raschauer}, AllgVerwR\textsuperscript{3} (2009), Rz 1\,424.}

\end{document}

Link to the PDF is here. It compiles, it validates as PDF/A, but I have this in my data:

Answer 1

hyperxmp is quite eager to add all info it can get to the metadata. And here it gets all fonts declared in the document (and not only the used fonts).

You can disable the whole font section with

\makeatletter
\renewcommand*{\hyxmp@xmptpg@schema}{%
  \ifLuaTeX
    %\luadirect{write_xmp_font_list(\the\hyxmp@cct)}% disable this
  \fi
  \hyxmp@add@simple{xmpTPg:NPages}{\@pdfnumpages}%
}
\makeatother

But imho it would be good if this were optional and more specific to the actually embedded fonts.