Shulker tracking player while using invisibility potion

Not sure if it's an intended feature to the game but when I'm just walking around the said shulker the shulker does not target me and stays docile like any other mob but as soon as I get close to the shulker it can somehow see me can someone tell me if this is a bug or if it's intended I'd be very grateful (in the screenshots provided you can clearly tell I have invisibility with regeneration just so I don't die from the shulker bullets + fall damage and as soon as I get close to the shulker it notices me and start's shooting it's projectiles.)