[BUG] Vanishing Majordomo stun gives Overkill or Master of Subtlety buff for the rest of the raid

[Beakachu]

1. Current Behavior

1.1. Description

Vanishing at the correct time on Majordomo gives overkill so a permanent 30% increase to rogue's energy regen rate or master of subtlety which is permanent 10% increase to a rogue's damage

Given that vanish is a normal part of an assassination and subtlety rogue's rotation, and that good rogues will try and vanish stuns for uptime, this bug is very easy to trigger accidentally without knowledge of its existence.

An average Majordomo kill using the most popular strategy at time of writing will have around 10-12 stuns, so the chance of at least one lining up with the vanish cooldown is quite high.

It is also trivial to trigger this bug intentionally.

This bug persists beyond the end of the Majordomo fight so as long as the rogue doesn't enter stealth or leave the raid, this powerful buff can be taken to Ragnaros.

1.2. How to Reproduce

       1. Engage Majordomo
       2. Slightly before he transforms out of Cat/Scorpion into Night Elf form, cast vanish to avoid the stun.
       3. Observe overkill buff lasting permanently instead of being 20 seconds or Master of Subtlety lasting permanently instead of 6 seconds.

1.3 Source Material

https://classic.warcraftlogs.com/reports/1vLK3y8fD7PRVbc4#fight=18&type=auras&ability=58427 https://classic.warcraftlogs.com/reports/RKNx4tfWvmanCVwD#fight=17&type=auras&source=54&ability=31665

2. Expected Behavior

2.1. Description

Overkill buff should be 20 seconds. Master of subtlety should be removed 6 seconds after breaking stealth.

[Beakachu]

This also applies to Master of Subtlety which is permanent 10% damage.

In both MoS and Overkill's case this buff can be taken to Ragnaros so this is 2/7 fights where a rogue playing legitimately cannot compete with accidental or intentional abuse of this.