bug#29711: 25.2; mode-line distortion when using :box on mac os

[Adam Simpson]

The below is with emacs -Q.
Also, I left out a step, after step 2 move to the bottom of the document (M - 
>). The mode line will then become distorted. 

Apologies for the shoddy reporting.
> On Dec 14, 2017, at 2:28 PM, Charles A. Roelli <charles@aurox.ch> wrote:
> 
>> From: Adam Simpson <adam@adamsimpson.net>
>> Date: Thu, 14 Dec 2017 13:20:20 -0500
>> 
>> 
>> 1. Paste and then evaluate the following in the *scratch* buffer:
>> (set-face-attribute 'mode-line nil
>>                    :foreground "white"
>>                    :background "red" 
>>                    :box '(:line-width 5 :color "red"))
>> (setq-default mode-line-format (list 
>>              '(:eval mode-line-position)
>>              mode-line-modes))
>> 2. Open a long file that has thousands of lines. I used ivy.el which is
>> around 4k lines.
>> 
>> 3. Observe the mode-line is "distorted" like so: 
>> https://i.imgur.com/qxAsdfm.png
>> 
>> 
>> 
>> In GNU Emacs 25.2.1 (x86_64-apple-darwin16.6.0, NS appkit-1504.83 Version 
>> 10.12.5 (Build 16F73))
>> of 2017-08-09 built on d12frosted.local
> 
> Doesn't happen here on macOS 10.6.  (For a "long file", I used M-x
> find-library simple RET).  Could you please try from emacs -q?