I had a short talk about this with a mod in the showdown help chat, and they told me it seemed worth reporting here: It looks like Meloetta's Pirouette form uses its special attack to do damage with tera blast, despite physical being higher.
Someone else tested in the calculator as well afterwards, agreeing with the statement of being bugged.
Someone else tested in the calculator as well afterwards, agreeing with the statement of being bugged.