This is a bug that applies to:
Version 5.0 (5.1.20725.935, 7/25/2012)
(also applies to previous versions)
You can't always copy a toolbar button from one toolbar to another using the ctrl drag method.
Steps to reproduce:
Ctrl click and drag a button from a docked toolbar to a floating toolbar. When the drag icon changes from the red crossed out circle denoting can't copy here to can copy here, release the mouse.
Caveats:
Most times it does not work the first time, but will work on subsequent attempts, but sometimes you can on the first try.