Parental Controls not working AC5300

Hi. I've enabled the parental controls on my router to block YouTube via the "Streaming and Entertainment" -> "Media Streaming" as documented, hitting Apply, but YouTube still loads fine, and videos are still playable. I've tried it on a couple of different computers on the network with the same result. Am I missing something perhaps?

I'm on firmware version: 3.0.0.4.384_82072

Thanks very much!