Employee's time entries are using the overtime rates on an overhead project. How to prevent that?
This happens if you have set Core to automatically evaluate overtime by checking the option Automatic overtime in Employees > General > Dates & Hours. This option marks the time entries as overtime automatically and causes the bill rate to update to the overtime rate set for the employee when the time logged exceeds the standard working hours. Uncheck this rule if you do not want the rates to update automatically. Check the Core Help for details.