Dirty_Player, the artifact's functionality is described in the artifact's description. I quote: "neutralizes the natural magic resistance of ALL creatures on the battlefield." No other conditions are specified.
The bug described by BaG2, I encountered in earlier versions of the launcher (a year and a half ago). If you believe that the artifact works differently, it would be worth providing a link to the source material to determine the truth and close the issue.
And what is the description in the screenshot? Does the highlighted part refer to HotA or some other mod?
(Василь Симоненко. Люди – прекрасні)