When a resource changes department the cost plan still reflects the actuals in the old department.
This is working as designed as the actual costs are historical records.
Even if a WIP adjustment is done, the department will not update to the resource's new department.
Release : ALL
Component : CA PPM SAAS FINANCIAL MANAGEMENT
The only way to get the actual costs to the new department would be to reverse the current transactions and manually enter them again as 'New' so they will pick up the new employee department.