Bug: Always returning "last task fails" on calling on_failure_callback_name

[bodhwani]

On defining on_failure_callback_name and on_failure_callback_file, if the very first task (say task1) fails, context["ti"] always return the instance of last task defined in the DAG.

Eg: task1 >> task2 >> task3

If task1 fails, context["ti"] is always returning task3 instance.
If task1 succeed and task2 fails, context["ti"] returns task3 instance.

def custom_failure_function(context):
    ti = context["ti"]

I think thats a bug. If it's not a bug, how can I get the failed task's instance?