Word -> EPUB Chapter titles blank for Headings using Word's {TC...} codes

I'm not sure if I'm just missing something or if this is a bug or missing feature around an admittedly rarely used feature of Word.

Here's the most common use case of this rare scenario:

Each chapter has a picture for the title of the chapter with the text of the chapter title in a stylized graphic. In order for the Word TOC to still generate correctly, you use Word codes like this {TC "Chapter 1. This is the first chapter" \1 1}. This is set to Hidden in Word so only the graphic is visible when printing.

Armed with that, in Heading 1 style Word can generate the TOC using the text, "Chapter 1. This is the first chapter".

However, upon converting this Word document to EPUB, Calibre shows this in the EPUB-generated TOC as "(Untitled)" including the parentheses. I find this odd, because Calibre obviously tries to find the chapter titles using the Heading styles, even when there is no Word TOC, but it seems to always fail in scenarios like this.

Is there a work-around or change needed to the document in Word for this to work for Calibre, or is this just a missing element in the DOCX -> EPUB conversion?

Thanks,
Colin