Assignee changed on task board close transition

The ability to move an issue from the in progress column to done with options for close or resolve plus the ability to automatically zero out estimate is very nice . However, as the pictures indicated, the operation re-assigned the issue for some unknown reason . The new assignee happens to be the default assignee for issues. For this project, we use Default assignee = project lead and Paul Smith is the project lead in this case. Other notes, the Auto check box is not checked.