Can't map multiple host ports to same container port

[cccCody]

Description

Steps to reproduce the issue:

1. create a compose file with multiple host ports mapped to the same container port, e.g.

services:
  redis_7001:
    ports:
      - "7001:7001"
      - "7002:7001"
      - "7003:7001"

2. run docker compose -f redis.yml up -d
3. list the ports: docker port development_redis_7001_1

Describe the results you received:
only the last host port (7003) is mapped to container port 7001:

7001/tcp -> 0.0.0.0:7003
7001/tcp -> :::7003

Describe the results you expected:
host ports 7001-7003 are all mapped to container port 7001 (this works with the old docker-compose (with the dash))

7001/tcp -> 0.0.0.0:7003
7001/tcp -> :::7003
7001/tcp -> 0.0.0.0:7002
7001/tcp -> :::7002
7001/tcp -> 0.0.0.0:7001
7001/tcp -> :::7001

Additional information you deem important (e.g. issue happens only occasionally):

Output of docker version:

Client:
 Cloud integration: 1.0.14
 Version:           20.10.6
 API version:       1.41
 Go version:        go1.16.3
 Git commit:        370c289
 Built:             Fri Apr  9 22:46:57 2021
 OS/Arch:           darwin/amd64
 Context:           default
 Experimental:      true

Server: Docker Engine - Community
 Engine:
  Version:          20.10.6
  API version:      1.41 (minimum version 1.12)
  Go version:       go1.13.15
  Git commit:       8728dd2
  Built:            Fri Apr  9 22:44:56 2021
  OS/Arch:          linux/amd64
  Experimental:     false
 containerd:
  Version:          1.4.4
  GitCommit:        05f951a3781f4f2c1911b05e61c160e9c30eaa8e
 runc:
  Version:          1.0.0-rc93
  GitCommit:        12644e614e25b05da6fd08a38ffa0cfe1903fdec
 docker-init:
  Version:          0.19.0
  GitCommit:        de40ad0

Output of docker context show:
You can also run docker context inspect context-name to give us more details but don't forget to remove sensitive content.

default

Output of docker info:

Client:
 Context:    default
 Debug Mode: false
 Plugins:
  app: Docker App (Docker Inc., v0.9.1-beta3)
  buildx: Build with BuildKit (Docker Inc., v0.5.1-docker)
  compose: Docker Compose (Docker Inc., 2.0.0-beta.1)
  scan: Docker Scan (Docker Inc., v0.8.0)

Server:
 Containers: 4
  Running: 4
  Paused: 0
  Stopped: 0
 Images: 9
 Server Version: 20.10.6
 Storage Driver: overlay2
  Backing Filesystem: extfs
  Supports d_type: true
  Native Overlay Diff: true
  userxattr: false
 Logging Driver: json-file
 Cgroup Driver: cgroupfs
 Cgroup Version: 1
 Plugins:
  Volume: local
  Network: bridge host ipvlan macvlan null overlay
  Log: awslogs fluentd gcplogs gelf journald json-file local logentries splunk syslog
 Swarm: inactive
 Runtimes: io.containerd.runc.v2 io.containerd.runtime.v1.linux runc
 Default Runtime: runc
 Init Binary: docker-init
 containerd version: 05f951a3781f4f2c1911b05e61c160e9c30eaa8e
 runc version: 12644e614e25b05da6fd08a38ffa0cfe1903fdec
 init version: de40ad0
 Security Options:
  seccomp
   Profile: default
 Kernel Version: 5.10.25-linuxkit
 Operating System: Docker Desktop
 OSType: linux
 Architecture: x86_64
 CPUs: 6
 Total Memory: 5.807GiB
 Name: docker-desktop
 ID: JA57:OAK7:GUZY:FC2D:5JCE:LSUW:DIOV:DZSZ:SQOZ:XGKG:643H:HGEI
 Docker Root Dir: /var/lib/docker
 Debug Mode: false
 HTTP Proxy: http.docker.internal:3128
 HTTPS Proxy: http.docker.internal:3128
 Registry: https://index.docker.io/v1/
 Labels:
 Experimental: false
 Insecure Registries:
  127.0.0.0/8
 Live Restore Enabled: false