postgresql full text proximity (`<->`) search on json document

I'm experiencing some unexpected behaviour for certain word combinations trying to use full text search on a json(b) document. Perhaps my understanding of text search is is incorrect or maybe this is a known bug.

Here's a simple example:

-- searching on text, expected true, query returned true
select to_tsvector('the quick brown fox jumped over the lazy dog')             
       @@ to_tsquery('fox <-> jump');
 ?column?
----------
 t
(1 row)

-- searching json, expected true, but query returns false
select to_tsvector('{"example": ["the quick brown fox", "jumped over the lazy dog"]}'::json) 
       @@ to_tsquery('fox <-> jump');
 ?column?
----------
 f
(1 row)

The unexpected behaviour seems to only happen across text elements for certain words, for instance, searching for fox <-> over works in the following example.

-- expected this to be true, and I get true back
select to_tsvector('["jumped the quick brown fox", "over the lazy dog"]'::json) 
       @@ to_tsquery('fox <-> over');
 ?column?
----------
 t
(1 row)

and similarly, if fox jumped were in the same text element, then the query returns true, as expected.

select to_tsvector('["the quick brown fox jumped", "over the lazy dog"]'::json) 
       @@ to_tsquery('fox <-> jump');
 ?column?
----------
 t
(1 row)

postgresql / system version tested on:

select version();
                                                    version
---------------------------------------------------------------------------------------------------------------
 PostgreSQL 10.1 on x86_64-apple-darwin15.6.0, compiled by Apple LLVM version 8.0.0 (clang-800.0.42.1), 64-bit
(1 row)

Copyright Notice：Content Author:「Haleemur Ali」，Reproduced under the CC 4.0 BY-SA copyright license with a link to the original source and this disclaimer.
Link to original article：https://stackoverflow.com/questions/57763985/postgresql-full-text-proximity-search-on-json-document