normal maps not working properly on uvchannel >0

Hi guys,

I just found out that normal maps are not working as intended if not used on uvchannel0 but 1 or above instead. It’s not an issue of a flipped green channel but seems to be a more general issue/bug?

Imgur

green: normal map on uvchannel0

red: normal map on rotated uvchannel1 , light direction does not match by 90 degrees (see red arrow from directional light)

seems solved but not yet documented as far as I can see? Tangents only calculated on UV0? - Rendering - Unreal Engine Forums

although switching to global itself breaks normal map behavior so I guess there is some work necessary to get this in a proper shape. documentation would be welcome for this feature!