UserAgent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_13_5) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/66.0.3359.81 Safari/537.36

Steps to reproduce the problem:
1. open a video on youtube
2. maximize window to full screen
3. try to maximize video to fullscreen

What is the expected behavior?
for video to stay maximized

What went wrong?
it tries to maximise but returns to window mode

Did this work before? N/A 

Chrome version: 66.0.3359.81  Channel: beta
OS Version: OS X 10.13.5
Flash Version: 

chrome://flags/#enable-content-fullscreen is enabled
works fine if chrome window is not in a full desktop window