The extra arguments required in the /clone filtered do not show in the help menu, and also do not show when some necessary additional arguments are not included.

Steps to Reproduce:
Simply by typing:

/clone 1 1 1 2 2 2 3 3 3 filtered

you will receive an error message which should give your the correct syntax in red, and you get this:
/clone <x1> <y1> <z1> <x2> <y2> <z2> <x> <y> <z> [mode].
The command you just typed includes all and only all the arguments listed in the red syntax, but is still failing.

The /clone filtered command requires the person executing it to have:
/clone <x1> <y1> <z1> <x2> <y2> <z2> <x> <y> <z> filtered mode2 filteredblock
and there should be a separate syntax for the /clone filtered command which includes these special arguments:
/clone <x1> <y1> <z1> <x2> <y2> <z2> <x> <y> <z> [mode1] [mode2] [filteredblock]