Chrome Version:67.0.3386.1
OS: Win 10

Note that this does not occur on Mac.
And this issue has been around for a long time. The first report was on M43, and it probably existed before that.

What steps will reproduce the problem?
1. cast a tab playing a vimeo.com video.
2. open a second tab to any page.
3. return to the tab playing the vimeo video and click full screen on the video.
4. pull that tab out.

What is the expected result? Fullscreen-in-tab continues, and the video can properly exit fullscreen mode.

What happens instead? At this point, the fullscreen-in-tab feature is broken in this tab. Even if you stop and restart casting, reload the page, etc. The video won't go full screen on the receiver or the sender (while casting or not), and there are small pillar boxed grey bars on the sender site.