This is currently expected. It's a limitation with this new change tracking report that we are working on improving.
This has been mentioned before and it's something we are working towards supporting. You'll be able to query your account manager on this feature’s development 😁️
In the meantime you may generate an Employee data changes report instead as this will give you the option to track the FTE - you will need to ensure that the FTE field is selected on the column picker.