Yeah, it's odd, and I don't know yet why there's a difference in behavior here between compact and standard tabs.
I don't think the screen resolution is a factor in causing the bug, but it was a required condition for me to at least reproduce it. I generally have my monitor at a higher resolution and because of that, the popover always had space to be shown on the left or the right - and it would not show up as a floating window ever.
By looking at your video, I figured that it is getting shown as a floating window because of lack of space, and that's what helped me reproduce it.
