dd tool: program vs. manual contradiction

[Volker Paul]

Hello,

I found what I see as a contradiction between 
the dd program error output and its manual.

info dd extract:
    `sync'
    Pad every input block to size of `ibs' with trailing zero
    bytes.  When used with `block' or `unblock', pad with spaces
    instead of zero bytes.

I read this as: sync can be used with unblock.
But I get the error message:

echo 000100020003 | dd cbs=4 conv=sync,unblock
dd: only one conv in {ascii,ebcdic,ibm}, {lcase,ucase}, {block,unblock},
{unblock,sync}

which I read as: unblock and sync can't be used together.

What is true?

(What I wanted to do is: 
Convert a file with fixed block size, here 4 bytes,
to one with every block ended with \n:
0001
0002
0003
)

Please notify me if you find an answer,
as I will inform you if I find out more myself.

Thanks,

Volker Paul