Set Load/Save to "ODF 1.4" so that it writes strict ODF. Take a text document and write some text. Assign a character style to a single word. Enable recording of changes (Menu Edit > Track changes). Assign a different character style to the same word. Save the document. Inspect the saved document. You will find an attribute "style-name" in the element <text:format-change> in the part content.xml. But the <text:format-change> element has no attributes. In extended mode, LibreOffice writes a "loext:style-name" attribute. But in strict mode it must not write an attribute at all.
I'll look at this.
Miklos Vajna committed a patch related to this issue. It has been pushed to "master": https://git.libreoffice.org/core/commit/5248afb9b630b5902936ea8a2f5c87248cb36dd3 tdf#168321 sw format redline, direct: fix ODF strict export It will be available in 26.2.0. The patch should be included in the daily builds available at https://dev-builds.libreoffice.org/daily/ in the next 24-48 hours. More information about daily builds can be found at: https://wiki.documentfoundation.org/Testing_Daily_Builds Affected users are encouraged to test the fix and report feedback.
Not writing the attribute is one problem, but then we should also not writer that otherwise unused autostyle, now both are done, I think.
Miklos Vajna committed a patch related to this issue. It has been pushed to "libreoffice-25-8": https://git.libreoffice.org/core/commit/6de684d777ccfb2a1b6f43081ca7fb53115e21d0 tdf#168321 sw format redline, direct: fix ODF strict export It will be available in 25.8.2. The patch should be included in the daily builds available at https://dev-builds.libreoffice.org/daily/ in the next 24-48 hours. More information about daily builds can be found at: https://wiki.documentfoundation.org/Testing_Daily_Builds Affected users are encouraged to test the fix and report feedback.