Oh, i forgot about browser details.
Firefox 77.0.1 (x64) on Windows 10 Insider Preview.
Also i can reproduce this behavior in Safari on mac OS 10.15 Catalina.
Thank you for reporting this issue, it has now been resolved. We are aiming to include any changes that have been made in a future XF release (2.2.0 Beta 4).
Change log:
Ensure that the preview area contains floating elements