BUG #15751: Unexpected behaviour at plainto_tsquery funciton

The following bug has been logged on the website:

Bug reference:      15751
Logged by:          Ozan Gerdaneri
Email address:      ozan.gerdaneri@gmail.com
PostgreSQL version: 11.0
Operating system:   win 10
Description:

Hi, 
My query is like this : 
.......
WHERE to_tsvector(COALESCE("blog"."name" )) @@ (plainto_tsquery("cat")) =
true

That is, I am searching for the word "cat" in name column. But the following
error is given. Why is    plainto_tsquery is looking for a column name?
                                                             ^
********** Error **********

ERROR: column "cat" does not exist
SQL state: 42703
Character: 511