BUG #16318: The default tablespace of a table and index is not inheriting the tablespace of database

The following bug has been logged on the website:

Bug reference:      16318
Logged by:          Jackey
Email address:      jackeylhm@gmail.com
PostgreSQL version: 11.6
Operating system:   Ubuntu
Description:

I created a table and an index without specifying a tablespace name, and
expect the table and index will use the database's tablespace.  But I found
the table and index is using the server's setting default_tablespace,
instead of the database's tablespace. Is this a bug? or this is the expected
behavior? I come from an Oracle DBA 's background, expecting all objects
created in a database will inherit the tablespace's setting of the database.