MIGO locks table after posting document

Hi Everyone,

I have an issue, that when we manually post a GR document in MIGO (get document number), system keeps locking tables (EKPO, MARC, MBEW, MCHA) till the time I exit from the transaction.What do you think is it correct? I checked, and waited for 20 minutes, but it was still locked. I tried to find SAP note, but didn't find one which is relevant for me. Using SAP ECC 6.0 release 605.

I would like to start a workflow, which post IR automatically, but as table is locked, it's not possible.

Thanks for your advice,

Tamas