Hi guys, I have two tasks in a DAG, t1 and t2. It used to be t2.set_upstream(t1) and now I want to refactor the logic by setting t1.set_upstream(t2). However, when I try to run this DAG, it either will try to run two tasks simultaneously or it will try to run t2 first and towards the end, it will also run t1 before t2 finishes. I am very confused about this behavior. Am I missing something here? I am using Airflow 1.8.1.