ExportFDF tool skips FDF from annotations

I have a PDF which contains lots of comments, which I want to export as XFDF. (Currently, this is done manually by firing up Acrobat, going to the Comment tool, and picking Export all to Data File)

If I use the org.apache.pdfbox.tools.ExportFDF tool, I get a FDF with no comments in. If I tweak it to use saveXFDF instead of saveFDF, I get an almost-empty XFDF with no comments either

From some limited research, it seems that the tool only handles the form-based FDFs, not the annotation-based FDFs. Ideally it would be extended to handle both.

In case it helps, attached is a simple 1 page PDF with 2 comments in, and the XFDF you get if you export the comments in Acrobat