It seems that by default nginx does not handle that HTTP code.

I just tried the following:
HEAD / HTTP/30.00
User-Agent: lollipop
Host: [EDITED]
Accept: */*

HTTP/1.1 200 OK
Server: nginx
Date: Tue, 04 Aug 2015 23:27:43 GMT
Content-Type: text/html; charset=UTF-8
Connection: keep-alive
Strict-Transport-Security: max-age=15984000

​So if you overload the status code with 505, the reason won't change and
still be 'OK'.​
​That would explain why you saw '505 OK' which is an heresy...​
---
*B. R.*

On Wed, Aug 5, 2015 at 1:25 AM, nginxuser100 <nginx-forum@nginx.us> wrote:

> Thank you Francis. The body content did the trick ... not as aesthetically
> pleasing to the eyes as the NGINX's "hard-coded reason phrase", but it is
> better than a blank page.
> I did not understand what you meant by a config to control the reason
> phrase.
> Thanks again.
>
> Posted at Nginx Forum:
> http://forum.nginx.org/read.php?2,260754,260761#msg-260761
>
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