Cannot provide parameters to 'Launch Stack' operation in horizon via env file

Issue

In Horizon, upon creation of a new stack, the environment variables are not read from the provided environment file and the user is asked to give the variables manually once more. The following environment file is being used:

parameters:
    public_network: 1111eeee-bbbb-aaaa-cccc-dddd33224444
    gateway_ip: 10.1.1.1

    kcs_img: image-name
    kcs_flav: flavor-name
    linux_img: image-name
    linux_flav: flavor-name

Try to create a new stack:

Provide stack definition and environment file:

Verify that parameters do not show up: