This seems like an ok feature, but it needs a lock so you can force tabs to stay docked if you want them to. Or maybe just have "undock" in the right click menu.
I can also get them to undock when simply mousing fast. It seems like the pull detection is a bit slow. This is most noticeable in a remote desktop session where the mouse is only updated occasionally on the host. It's almost a certainty to undock a tab when mousing on remote desktop (and clicking between tabs).