This is intended behavior and is because this control serves a dual purpose as a button, to make it easy to submit the task, a dropdown list.
When a new Task is created, the status option only shows "Submit" instead of "Not started". There's no drop-down option from the "Submit" button.
When a user creates a task, assigns it to themselves, and updates the status from "Not Started" to "In Progress", the blue "Submit" button continues to display by design. However, the task’s true status—In Progress—is reflected in both the task activity feed and the task grid view.
However, if the task is assigned to another user, changing the status from "Not Started" to "In Progress" updates the task's status to "In Progress" on the detail view, activity feed, and grid view.
