I clicked "Complete Project" on the "Edit project" screen, it asked me if I am sure, I answered Yes, then my project disappeared. Does "complete" equals "delete"? Is there a way to undo a "complete project" operation?
It hides the project and the tasks/milestones it include from most screens. Just click on the link below the project list on the overview page (X completed projects) to list the completed ones and re-open a completed project.
