[O] Bulk re-scheduling in agenda view

[Michael Hoffman]

I am bulk re-scheduling items in an agenda view. I would like all the 
selected items to be re-scheduled to a year later from their current 
scheduled date. The org manual 
<https://orgmode.org/manual/Agenda-commands.html> seems to indicate this 
is possible using double plus:

> Schedule all items to a new date. To shift existing schedule dates by
> a fixed number of days, use something starting with double plus at the
> prompt, for example ‘++8d’ or ‘++2w’.

When I try this, however, I always get re-scheduling from the current 
date. I am using Org mode version 9.1.6 (9.1.6-48-gfe7619-elpa). Here's 
how to reproduce:

1. Create minimal.org.el:

(setq debug-on-error t
      debug-on-signal nil
      debug-on-quit nil)
(add-to-list 'load-path "c:/Users/micha/.emacs.d/elpa/org-20180212")

2. emacs.exe -Q -l minimal-org.el

3. Create a test.org buffer:

* TODO Task
  SCHEDULED: <2018-01-01 Mon>

4. Add it to the agenda files list with C-c [.

5. M-x org-agenda RET t results in

Global list of TODO items of type: ALL
Available with ‘N r’: (0)[ALL] (1)TODO (2)DONE
  test:       TODO Task

6. Move down to TODO Task and type m to mark

7. B s (bulk schedule). The minibuffer will state:

(Re)Schedule to Date+time [2018-02-11]: [cursor] => <2018-02-11 Sun>

8. ++1y. The right part of the minibuffer now states

<2019-02-11 Mon>

I expected <2019-01-01 Tue>

9. RET.

The task is now rescheduled to <2019-02-11 Mon> rather than <2019-01-01 
Tue> as initially expected.

Am I doing something wrong here?

Thanks,
Michael Hoffman