Hells' Gate - Taking unavoidable vulnerability stack from Genbu

Date & Time: August 29th, 2018
Frequency: Almost always
World name: Behemoth
Character name: Samias Lemura
Monster name: Genbu
Class/Level: 70
Party or solo: Party
Area and coordinates: Hells' Lid Dungeon
Steps:
1. Fight Genbu and trigger him to switch to Chelonian Gate with Sinister Tide markers still on the field.
2. If you're standing on an arrow marked tile, even if it would have been safe from the Sinister Tide water ball, you are hit with a vulnerability stack when you are knocked back.