BUG #15172: Postgresql ts_headline with <-> operator does nothighlight text properly

The following bug has been logged on the website:

Bug reference:      15172
Logged by:          Ngigi Waithaka
Email address:      ngigi@at.co.ke
PostgreSQL version: 10.3
Operating system:   Linux
Description:

I have a noticed a likely bug when using ts_headline with the <-> operator

Assuming the following query:

SELECT ts_headline('English','This Commercial Bank does not have any Equity
in Europe but European Commercial Bank does', 
                    phraseto_tsquery('English','European Commercial
Bank')::tsquery);

The returned result is:
This <b>Commercial</b> <b>Bank</b> does not have any Equity in Europe but
<b>European</b> <b>Commercial</b> <b>Bank</b> does

This highlights the words Commercial & Bank separately in addition to
European Commercial Bank.

However, the correct output expected should be:
This Commercial Bank does not have any Equity in Europe but <b>European</b>
<b>Commercial</b> <b>Bank</b> does

Which only highlights *European Commercial Bank* due to the <-> operator in
phraseto_tsquery.

SELECT phraseto_tsquery('English','European Commercial Bank');
returns 'european' <-> 'commerci' <-> 'bank' as expected indicating the
problem is with ts_headline function.

Regards
NgigiW