vscode containerEnv not working in mounts

I'm using the vscode command Remote-contains: Open Folder in container...

I'm trying to mount bind a file into the docker container.

~/.config/dart/pub-tokens.json

The host file is under my HOME directory and I need it mounted in the same location within the container's HOME directory.

Here is my mount command from the vscode devcontainer.json

"mounts": [
        "source=${localEnv:HOME}/.config/dart/pub-tokens.json,target=${containerEnv:HOME}/.config/dart/pub-tokens.json,type=bind,consistency=cached",
        
    ]

Note the 'containerEnv' in the target clause.

Launching the container via the vscode Remote-contains: Open Folder in container... produces the following error: (for readability I've added some newlines)

Start: Run: docker run --sig-proxy=false -a STDOUT -a STDERR 
--mount type=bind,source=/home/bsutton/git/onepub/onepub,target=/workspaces/onepub 
--mount source=/home/bsutton/.config/dart/pub-tokens.json,target=${containerEnv:HOME}/.config/dart/pub-tokens.json,type=bind,consistency=cached 
--mount source=/home/bsutton/.onepub/onepub.yaml,target=${containerEnv:HOME}/.onepub/onepub.yaml,type=bind,consistency=cached 
--mount type=volume,src=vscode,dst=/vscode -l devcontainer.local_folder=/home/bsutton/git/onepub/onepub 
--entrypoint /bin/sh vsc-onepub-7ff341664d5755895634c2f74983ff45-uid -c echo Container started

docker: Error response from daemon: 
invalid mount config for type "bind": invalid mount path: '${containerEnv:HOME}/.config/dart/pub-tokens.json' mount path must be absolute.

It would appear that vscode isn't expanding the the containerEnv.

If I replace containerEnv it with localEnv it does get expanded (but the wrong path).

i.e. the following works:

"mounts": [
        "source=${localEnv:HOME}/.config/dart/pub-tokens.json,target=${localEnv:HOME}/.config/dart/pub-tokens.json,type=bind,consistency=cached",
        
    ]

Here is the complete devcontainer.json

// For format details, see https://aka.ms/devcontainer.json. For config options, see the README at:
// https://github.com/microsoft/vscode-dev-containers/tree/v0.245.0/containers/ubuntu
{
    "name": "Ubuntu",
    "build": {
        "dockerfile": "Dockerfile",
        // Update 'VARIANT' to pick an Ubuntu version: jammy / ubuntu-22.04, focal / ubuntu-20.04, bionic /ubuntu-18.04
        // Use ubuntu-22.04 or ubuntu-18.04 on local arm64/Apple Silicon.
        "args": { "VARIANT": "ubuntu-22.04" }
    },

    // Use 'forwardPorts' to make a list of ports inside the container available locally.
    // "forwardPorts": [],

    // Use 'postCreateCommand' to run commands after the container is created.
    // "postCreateCommand": "uname -a",

    // Comment out to connect as root instead. More info: https://aka.ms/vscode-remote/containers/non-root.
    "remoteUser": "vscode",
    "features": {
        "git": "latest",
        "github-cli": "latest"
    },
    "mounts": [
        "source=${localEnv:HOME}/.config/dart/pub-tokens.json,target=${containerEnv:HOME}/.config/dart/pub-tokens.json,type=bind,consistency=cached",
        "source=${localEnv:HOME}/.onepub/onepub.yaml,target=${containerEnv:HOME}/.onepub/onepub.yaml,type=bind,consistency=cached"
    ]
    
}