You have a stand-alone task that has no dependencies.
If you set Status to "Not Started", the float is calculated as 40 days and the task is not marked as being critical, which is correct.
However, when you change the status to "Started" the Early Start and Late Start are set as equal, which results in 0 float and puts the task on the critical path. This is incorrect as the status should not affect the float and it should not be on the critical path.
All supported releases
Task is not set to fixed duration
Set the task to fixed duration and auto-schedule again.