List of steps to reproduce (step by step, including full links if applicable):

• edit MediaWiki:Scribunto-doc-page-header and add a category

What happens?:
The category is present in the MW page itself, but is missing from any module /doc subpages

What should have happened instead?:
The category should be present in all module /doc subpages

For comparison, other Scribunto MW pages, e.g. MediaWiki:Scribunto-doc-page-show work normally, any added categories will show on all module pages.
Example:

• hrwiki Scribunto-doc-page-show adds a "Lua moduli s dokumentacijom" category and hrwiki Module:Namespace_detect shows this category
• hrwiki Scribunto-doc-page-header adds a "Dokumentacijske podstranice imenskog prostora Modul" category and hrwiki Module:Namespace_detect/doc does not show this category