The same happens on Safari meaning that it is either a WebKit bug or Youtube is simply making the user experience on webkit browsers worse.
If you believe it's the former, report the issue here: https://bugs.webkit.org/
As a workaround, you can middle click the video title as that will still open in a new tab. As soon as you hover over the video and the preview starts playing, middle clicking the video will open it in the current tab.
Curiously, if you middle click on a video thumbnail when Orion/Safari is not the active window, the video will open in a new tab.
