BUG #15488: Unexpected behaviour of to_tsverctor and ts_query

The following bug has been logged on the website:

Bug reference:      15488
Logged by:          Nikolajs Arhipovs
Email address:      nikolajs.arhipovs@gmail.com
PostgreSQL version: 9.6.8
Operating system:   Linux, kernel 4.18.16-arch1-1-ARCH
Description:

I am trying to do prefix search of emails using full text search. Emails
sometimes contain dot symbols.
Now, select to_tsquery('simple', 'thing.a:*'); returns a single term as
expected but 
select to_tsquery('simple', 'the.thing.a:*')  suddenly tokenizes my search
expression into 'the.thing':* & 'a':*. At the same time select
to_tsquery('simple', 'the.thing.aa:*'); tokenizes as expected into a single
term.
Also select to_tsquery('simple', 'the.thing@gmail.com'); returns a single
term as expected, but select to_tsquery('simple', 'the.thing@gma:*'); splits
on @ char and returns two tokens.
This behavior is not covered in the official documentation.