我得到500（内部服务器错误），但仍显示json结果，为什么？

I have a test server and 2 test domains, but I get this problem but I can't explain. My server : Nginx PHP 5

Check status by Browser : chrome

> 505 error but still get result : 
>     
>         http://trangantravel.vn/autocomplete_deluxe/taxonomy/field_length/%20/10?term=&synonyms=0
>         
>         200 Status ok, same Ip
>         http://phutungoto.zapto.org/vi/autocomplete_deluxe/taxonomy/field_loai_phu_tung/%20/10?term=&synonyms=0

Can you explain why I still get result (json) meanwhile I get 500 error status?