postgres image (or Docker) ignores updates to .sql files but not .sh files in /docker-entrypoint-initdb.d??

I have a docker compose file that looks like this. (postgres:alpine is currently pointing at v10.3)

    version: '3'
    services:
      webapp:
        build: '.'
        ports: 
          - "8000:8000"
        networks:
          - db

      postgres:
        image: "postgres:alpine"
        environment:
          POSTGRES_PASSWORD: "password"
        volumes:
          - "./scripts:/docker-entrypoint-initdb.d"
        networks:
          - db
    networks: 
      db:

The scripts folder looks like this:

|- scripts
 |-- init.sh
 |-- init.sql

The Problem

My workflow for this project is progressive, so I add some SQL initialization data on my host OS, run sudo docker-compose down -v and then sudo docker-compose up. I did not update my user to not need the use of sudo for this scenario.

When I update the init.sh file, then these updates are reflected each time I run docker-compose up. The init.sql file however, only remembers the first "version" of this file. Any subsequent updates are ignored when running docker-compose up.

Things I tried

Tried sudo docker-compose up --renew-anon-volumes --force-recreate which also does not seem to help.
Tried pruning all the volumes with sudo docker volume prune. Does not help
Tried pruning the docker system with sudo docker system prune
What does work is if I copy the file and it's content to a new file name. Renaming the file does not work

So the question is simply, how do I get content updates of init.sql to be recognized by my docker compose setup?? I don't understand why changes to init.sh is picked up but changes to init.sql are ignored?

How to reproduce

Add the postgres section to a docker-compose.yml file
Add the scripts folder with an init.sh and init.sql file. The sql script can be anything, but below is what I used. The init.sh can have a bunch of echos.
Start container with docker-compose up
Make changes to the SQL file (e.g. add more insert statements or move table creation to the top)
Make changes to the .sh file
Run docker-compose down -v followed by docker-compose up
You will see in the logs that the updated init.sh script runs and an outdated version of init.sql runs!!

CREATE TABLE CUSTOMER (
    ID SERIAL PRIMARY KEY,
    NAME VARCHAR(200)
);

SELECT NULL AS "Starting to insert into table CUSTOMER";

INSERT INTO CUSTOMER(NAME) VALUES ('Shiraaz Moollatjie');

CREATE TABLE MAILING_LIST (
    ID SERIAL PRIMARY KEY,
    NAME VARCHAR(200)
);

SELECT NULL AS "Starting to insert into table MAILING_LIST";
INSERT INTO MAILING_LIST(NAME) VALUES ('myEmailAddress@gmail.com');

COMMIT;

docker-library / postgres

postgres image (or Docker) ignores updates to .sql files but not .sh files in /docker-entrypoint-initdb.d?? #439