In short - my trouble is:  I can't do it.

I've tried Command-C, etc (keystroke for cut and paste) - no go.  I've tried to hold down the Command key while dragging the entry to a new time - this almost works as it does indicate a little green "+" sign as if it recognizes it's supposed to be copying - but when I release the mouse key the entry just gets sucked back over to it's original time.  I realize if I release the command key too early it thinks it's just moving and not copying.

I've tried everything - what am I missing???

Many thanks - 
Brad