BUG #15493: Wrong name of fields/missing fields for the internal statistic

The following bug has been logged on the website:

Bug reference: 15493
Logged by: - -
Email address: frank(dot)buettner(at)mdc-berlin(dot)de
PostgreSQL version: 11.0
Operating system: CentOS 7.5
Description:

How to produce:
- Simple install pgsql 11 on CentOS from yum repo of postgresql.org
- init the cluster
- start the server
- wait some time

After some times, many errors are logged about not existing fields.
< 2018-11-08 14:21:59.820 CET >ERROR: column "procpid" does not exist at
character 132
< 2018-11-08 14:21:59.820 CET >STATEMENT: SELECT datname, datid, usename,
client_addr, '' AS state, COALESCE(ROUND(EXTRACT(epoch FROM
now()-query_start)),0) AS seconds,
procpid as pid, regexp_replace(current_query, E'[\n\r\u2028]+', '
', 'g' ) AS current_query FROM pg_stat_activity WHERE (query_start IS NOT
NULL AND current_query NOT LIKE '<IDLE>%') ORDER BY query_start, procpid
DESC;
< 2018-11-08 14:22:00.117 CET >ERROR: column "current_query" does not exist
at character 200
< 2018-11-08 14:22:00.117 CET >STATEMENT: SELECT COUNT(datid) AS current,
(SELECT setting AS mc FROM pg_settings WHERE name =
'max_connections') AS mc,
d.datname
FROM pg_database d
LEFT JOIN pg_stat_activity s ON (s.datid = d.oid) WHERE
current_query <> '<IDLE>'
GROUP BY 2,3
ORDER BY datname

When I look in the database I can see, that the field has other name:
postgres=# \d+ pg_stat_activity
View "pg_catalog.pg_stat_activity"
Column | Type | Collation | Nullable |
Default | Storage | Description
------------------+--------------------------+-----------+----------+---------+----------+-------------
datid | oid | | |
| plain |
datname | name | | |
| plain |
pid | integer | | |
| plain |

And pg_settings has no column current_query:
postgres=# \d+ pg_settings
View "pg_catalog.pg_settings"
Column | Type | Collation | Nullable | Default | Storage |
Description
-----------------+---------+-----------+----------+---------+----------+-------------
name | text | | | | extended |
setting | text | | | | extended |
unit | text | | | | extended |
category | text | | | | extended |
short_desc | text | | | | extended |
extra_desc | text | | | | extended |
context | text | | | | extended |
vartype | text | | | | extended |
source | text | | | | extended |
min_val | text | | | | extended |
max_val | text | | | | extended |
enumvals | text[] | | | | extended |
boot_val | text | | | | extended |
reset_val | text | | | | extended |
sourcefile | text | | | | extended |
sourceline | integer | | | | plain |
pending_restart | boolean | | | | plain |