Nostalrius Begins - Quality wow vanilla realm (1.12)

So when using Sinister strike I thought you lose 20% on dodge, miss, and parry. With talent you lose 8 ( 20% of 40) without lose 9 ( 20% of 45 ). I lose 7 on dodge and miss, and I lose all 40 on a parry. Is this accurate Vanilla or bugged?