The entire workflow fails if one of a join task inbound tasks fails

Example:

---
version: "2.0"

wf:
  output:
    continue_flag: <% $.get(continue_flag) %>

  task-defaults:
    on-error:
      - change_continue_flag

  tasks:
    task_a:
      action: std.fail
      on-success:
        - task_c: <% $.get(continue_flag) = null %>
        - task_a_process

    task_a_process:
      action: std.noop

    task_b:
      on-success:
        - task_c: <% $.get(continue_flag) = null %>

    task_c:
      join: all

    change_continue_flag:
      publish:
        continue_flag: false

It fails and the following output:

wf (d58c505d-1683-4947-b86f-8bf8e5ab8db8) [state=ERROR, state_info=Failed by tasks: ['task_a'], output={'result': "Failed by tasks: ['task_a']"}]
 task_b [id=3044ba57-3877-4ce1-80c1-64baf98d3468, state=SUCCESS, state_info=None, processed=True, published={}]
  std.noop [id=c05b2472-5db8-4cad-ae34-1a9a27c0e2e0, state=SUCCESS, state_info=None, accepted=True, output={'result': None}]
 task_a [id=d32ecfb0-c0f1-4247-9ced-2a31bbfd224e, state=ERROR, state_info=Failed to run action [action_ex_id=0ab484ba-2418-4b19-ba14-cac963065b64, action_cls='<class 'mistral.actions.action_factory.FailAction'>', attributes='{}', params='{}']
 Fail action expected exception., processed=True, published={}]
  std.fail [id=0ab484ba-2418-4b19-ba14-cac963065b64, state=ERROR, state_info=None, accepted=True, output={'result': "Failed to run action [action_ex_id=0ab484ba-2418-4b19-ba14-cac963065b64, action_cls='<class 'mistral.actions.action_factory.FailAction'>', attributes='{}', params='{}']\n Fail action expected exception."}]
 task_c [id=4feced3c-9bad-40c2-bfa5-6f262cef4947, state=ERROR, state_info=Failed by tasks: ['task_a'], processed=False, published={}]
 change_continue_flag [id=bfa0b538-d7ea-4276-954a-6c3f356fbf11, state=SUCCESS, state_info=None, processed=True, published={'continue_flag': False}]
  std.noop [id=3299e61f-afb6-4949-b370-6ec0f3ead67e, state=SUCCESS, state_info=None, accepted=True, output={'result': None}]