Youtube embed codes seen as 'dangerous_tags'

Good morning, I am new here but thought I should ask about this. I created a new page and embedded a Youtube video using this code:

<iframe src="//www.youtube.com/embed/hD-MBjzTT0A" width="560" height="315" frameborder="0" allowfullscreen="allowfullscreen"></iframe>

After saving this page I saw this notice in a green bar at the top of the page:
NOTICE: Grav found potential XSS issues in content: 'dangerous_tags'

I then removed the embed code and saved again and the warning had gone.

So for some reason Grav isn't liking the embedded code.

I am using Grav v1.6.0-rc.4 - Admin v1.9.0-rc.4 with quark v2.0.0-rc.2

I hope I have given the right information.
Cheers
Dave

OK as I said I am new to Grav, but I got this one sussed:
https://getgrav.org/blog/new-xss-protection

Indeed, and it should be, even though you can disable that behavior in settings. It's generally better that you use the YouTube-shortcode plugin.