I think I can explain the problem.
First, to intentionally drag a tab to a new window, click & drag ANY tab DOWNWARDS until it pops off the tab bar (a quarter way into the address bar (43px~ from the top of the browser window)).
You can also click & drag ANY tab to the beginning of the tab bar (left) and then continue dragging left until it pops off (63px from the left edge of the browser window (until you touch the edge of the letter 'u' in the word 'O Menu' AKA 11px to the left)).
Similarly you can click & drag ANY tab to the end of the tab bar (right) and then continue dragging right until it pops off (17px~ from the edge of the '+' button).
The PROBLEM arises when someone is trying to REARRANGE the order of the tabs to either the beginning or end of the bar, their fast movement and momentum of the mouse easily goes past the narrow 11px to the left and narrow 17px to the right of the tab bar. It can also happen when dragging left or right but the mouse moves more down while dragging, after all you only have 43px~ to work with.
Solution: only allow dragging DOWNWARDS to let the tab pop off the tab bar. Will be MUCH less of a headache.
My resolution is 1366x768, Win O48, maximised window.