Cross-referencing sections errors with EPUB

[JacekPardyak]

Hi,
I'm writing my book and noticed that in source of EPUB reference labels look like
<a href="#Een-beetje-verliefd">3.6</a>
while should be:
<a href="ch003.xhtml#Een-beetje-verliefd">3.6</a>
As a result my book (bookdown's book too) doesn't pass validation (https://www.ebookit.com/tools/bp/Bo/eBookIt/epub-validator) . On Google Play it doesn't rise error, but references don't work.

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[cderv]

Just for reference this is related to another EPUB check issue: #766