Project "Must Finish By" date must be the day after the required date?

I have found that I must set the Project "Must Finish By" date must be set to the day after the required date in order for that activity to have zero days of float.

Is this normal?

I have a schedule reviewer questioning why this is necessary.

See the screenshots below:

                                                                                                                                   

                                                                                                                                                     Total Float

         

Above: This is the last activity in the schedule with zero days of float. The required finish date for the project is 6-18-18

Below: The Project Must Finish By date must be set to 6-19-18 in order for the Finish date to be 6-18-18 with zero days of float.