Black and Pantone pdf export in Affinity Publisher issues

[grafemo]

Hi!
I am working on a book design and got to a strange issue.
I have a text set in black and have an illustration in two colors. Each color (black and Pantone) is a separate grayscale image.

But when I try to export my project to pdf, either I get the composite black on the text, either lose my color separation on illustration.

I've attached sample files and hope somebody can help me find a working solution.

colortesting.afpub colortesting-pdfx1a2003.pdf colortesting.pdf

[lacerto]

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