When you copy and paste a table, a view of the original table is created by default. However, if you want a copy that is not linked you can do so by selecting the Duplicate data instead option:
(note: this message pops up at the bottom of the Coda page)
To copy a table, select the table so that the entire table is outlined in blue.
Use the keyboard shortcut Crtl+C to copy it.
Click on the spot in the canvas where you want to paste it.
Use the keyboard shortcut Crtl+V to paste it.
By default, a view of the table will be pasted, but when the pop-up appears at the bottom of the screen, select "duplicate data instead."