Why are COMPOSE_PROJECT_NAME and -p ignored in docker-compose?

Question

Why are my COMPOSE_PROJECT_NAME and -p ignored in docker-compose?

I thought these were supposed to prepend the service names to help me organize my namespace but it seems that they are completely ignored.

Answer 1

Answering my own question to hopefully save someone else the effort.

I had used the container_name option n my docker-compose.yml. Seems like if you do that then the nifty -p flag does not apply.