So in addition to this only appearing in the emacs-mac port, it is also only in recent Org version. I now think this is related to the new feature of allowing multiple #+CAPTION lines, instead of just one #+CAPTION line.

  -k.

On Sun, Sep 28, 2014 at 12:41 AM, Ken Mankoff <mankoff@gmail.com> wrote:

* On 2014-09-28 at 00:27, Ken Mankoff wrote:
> * On 2014-09-27 at 23:45, Ken Mankoff wrote:
>> I find it strange that y'all can't re-create this since I can do it
>> with emacs -Q, although perhaps it is specific to the emacs-mac port.
>
> Just checked and it isn't in latest emacs HEAD. I'll submit a bug
> report to the emacs-mac project.

For record-keeping purposes, google, Bing, other people, and future
versions of me, this bug has been reported here:
https://github.com/railwaycat/emacs-mac-port/issues/59

  -k.