The syntax for /clone (seen by typing /help clone or just /clone) shows:

/clone <x1> <y1> <z1> <x2> <y2> <z2> <x> <y> <z> [mode]

when it should be:

/clone <x1> <y1> <z1> <x2> <y2> <z2> <x> <y> <z> [mode] [mode2]

because all filtration modes (replace, masked, filtered) can have a copying mode (normal, force, move) which can be inserted after the filtration mode. This additional mode should be shown in square brackets after [mode] as it is optional.