Transaction Accounting

We are having an issue in regards to costing in inventory.  Whe have a business unit that is generating inventory demand via ePro requisition and sourcing from inventory and entering MSR's within the inventory module.

The person creating the MSR or ePro requisition can be from various departmetns within the OU/BU.  It seems that when an MSR is generated that the only department that is costed for the expense is the one set up in the transaction accounting rules.  I thought that that default department would be overriden by the login of the person that was creating the MSR not hard coded to the department in the transaction accounting rules.