VSCode devcontainer docker login Error: Cannot perform an interactive login from a non TTY device

Question

I'm running some devcontainers in VSCode. Some are able to login to my docker registry and some aren't and I cannot work out what the difference is.

On the command line in a VSCode terminal I enter

echo $MY_REGISTRY_PASSWORD | docker login my-cloud-registry.io -u $MY_REGISTRY_USERNAME --password-stdin

and get back

Error: Cannot perform an interactive login from a non TTY device

But on other devcontainers, with the same configuration as far as I can see, it logs in without a problem.

There has to be some configuration difference, but I can find it.

Any ideas what configuration item I should be looking at?