JFFS/MTD and Raw access

[Damien GERANTON]

Hello,

I face a strange problem, i use MTD with JFFS and i want to clone my systeme
from one card
to another.
I thought that some think like :
dd if=/dev/mtd0 of=/master.img

and

dd if=/master.img of=/dev/mtd0

But it does not work, if after i do

dd if=/dev/mtd0 of=/test.img
diff test.img master.img
i says they are different.

Is it normal.

Is RAW acces really RAW ?

Do i miss some think ?

Thanks

PS : I use MTD on 2.2.17 kernel