Snowflakes dont atack but disable s undead

FM and I palyed a game he was undead i snowflakes. Then he attacked with boost and won first roll but didnt kept the boost. i havent attacked him but was only one using snowflakes. So it should have disabled it if attacked him but i never did until after he lost both boost. The boost was a prepaid not a free and and it was 2 boost maximum. 1 free 1 paid