The Cost of Booking can be duplicated due to the Resources Resource Rate Per Hour having 'Get the rates from the LABOUR RESOURCES shown below:' enabled. You can check if this option is enabled by doing the following:
Click Production then click Resource Maintenance.
Press F5 in the 'Resource Rate Per Hour>' column.
In the 'Planned Time - Labour' section you will see three radio buttons. If the 'Get the rates from the LABOUR RESOURCE shown below' radio button is ticked this will cause the cost to apply both the Machine and Labour costs.
