Theme inheritance and templates

Hi,

I have a problem with theme inheritance and templates override.

I have a theme "ThA" with specific Twig templates. Templates are declared in hook function ThA_theme().
I create a new theme "ThB" herited from "ThA" (I have set "base theme: ThA" in the ThB.info.yml file). In templates directory of ThB, I rewrite some Twig files overriding ThA ones (same name, same location).

Twig files from ThB are not used. I must explicitaly create a hook function ThB_theme() and declare each Twig file.

Did I forget something in my statement?

Thanks in advance,

Sylvain