You observe that when the setting "Automatically Add Staff Members As Investment Participant" is enabled, when you add a resource in the Staff tab in a project, the resource is also automatically added to the Participants list (as expected). However, if the resource is removed from the Staff tab, the Participant remains in the participants list.
Any Clarity supported release.
This is working as per the intended design.
This setting works one-way only: if set, the staff member will be added as participant, but if removed from Staff, the participant will remain unless it is manually removed.