Exchange rate differences between GR and IR

Hi Gurus,

i have a problem about a exchange rate differences beetween GR and IR. Customizing setting is done based on this logic (transaction OMRW, ERD setting = blank).

For example: Goods Receipt amount is $100 and the posting is made with exchange rate 0,8. When busy with MIRO the user change manually exchange rate from 0,8 to 1,0. Moreover, the user change item amount from $100 to $150.

When the user simulate the posting in MIRO, transaction KDM is not activated (used).

Is to be underline that if item amount is not change but it remains untouched, transaction KDM is used correctly.

The system is:

SAP ECC 6.0

Software component:  SAP_APPL     

Release:  600     

Level: 0016     

Highest support package: SAPKH60016     

Short description of software component: Logistics and Accounting

Have you any ideas about the reason of this malfunction?

Many thanks already in advance.

Stefano