122 return delivery excise invoice

HI,

I have diid GR with excise invoice caputre and post . here mat doc created and ex inv also posted..

later i did 122 for the same mat doc. , here mat doc created as well outgoing ex invoice also created automatically.

i didn't carried down J1IS ref to 122 mat doc.. but there is OTHR doc is created? how its createing automatically?

then why J1IS is recommendated for rtun dellivery. pls explain