unshelve emits "UserWarning: ProgressTask(0/3, msg='Merge phase') is not the top progress task ProgressTask(None/None, msg='')"

"bzr unshelve" seems to have a bug with the new progress bars:

$ bzr unshelve
Unshelving changes with id "3".
/home/andrew/code/bzr/bzrlib/ui/text.py:96: UserWarning: ProgressTask(0/3, msg='Merge phase') is not the top progress task ProgressTask(None/None, msg='')
  (task, self._task_stack[-1]))
/home/andrew/code/bzr/bzrlib/ui/text.py:96: UserWarning: ProgressTask(1/3, msg='Merge phase') is not the top progress task ProgressTask(None/None, msg='')
  (task, self._task_stack[-1]))
 M bzrlib/smart/message.py
 M bzrlib/smart/request.py
/home/andrew/code/bzr/bzrlib/ui/text.py:96: UserWarning: ProgressTask(2/3, msg='Merge phase') is not the top progress task ProgressTask(None/None, msg='')
  (task, self._task_stack[-1]))
All changes applied successfully.

There's nothing visible in the ~/.bzr.log file about it.