Greater Split: Vertical not destroying any combat pages?

[Voodoo Child]

Noticed this during Tanya's fight. At some point during the fight, she will use only 2 of her speed dice, one playing her mass attack and the other a normal card. You are evidently supposed to use Greater Split:Vertical on the normal card to destroy the mass attack, but when I did it, Tanya still got to use her mass attack.