When watching YouTube videos in fullscreen, the video is not displayed at full resolution?

So, I recently pulled up the "stats for nerds" on YouTube videos, and for some reason when watching a video at full 1080p resolution on my 1080p monitor, it's only being played back at 720p. The "dimensions" area on the stats is what resolution the video is BEING played at, while the "resolution" is what resolution the video is SET to be played at. As can be seen in the bottom right hand corner, it is indeed set to play at 1080p quality. Here is a link confirming my monitor setup, that it is, in fact, set to 1080p as well:

http://gyazo.com/72851332d4f80c80d6666d8cd2f1afb2

I find this odd, but not surprising because YouTube is very buggy and annoying, but I don't have an answer as to why it does this or how to fix it. I'm figuring that when going fullscreen, it's just like the other modes, and it's just another size of the player, and not actually going to fullscreen mode. Perhaps I'm wrong, but try it yourself and see if it happens. If you know why it might be doing this, then please, leave an answer on how to fix this.

Thanks in advance.