Cloud Formation parameter field doesn't seem to parse variables.

[John Thompson]

I'm trying to pass an ami_id as an environment variable with:

AmiId=${AMI_ID}

in the parameters field of the plugin.

When I look at the resulting stack, the plugin seems to be passing literally '${AMI_ID}' as the parameter value instead of ami-0283893 or whatever.

The documentation says it's supposed to parse environment variables.  Is there some trick to getting this to work, or is this a bug? If I run aws cloud-formation as a shell script with the environment variable, it seems to work fine.