Thanks for the demonstration video!
When you move "command 5" up there appears a blue line between the commands, and "command 5" stays in the position of the blue line releasing the button. For me that blue line does not appear, "command 4", "command 3" etc become blue instead (command 5 stays blue). When I get above the "New Dock" set (command 5 - command 1 set) the blue line appears and I can drop "command 5" where the blue line is.
I note that when you move "command 6" on the video this blue line does not appear.
I am using version 1.50.01 which I go when I downloaded two days ago. Windows 2000 professional in English, all updates done