Env variable not populated when sending request using newman

There is a difference in how Postman collection runner and newman work and Iā€™m not sure what is going on.
I have a request with two variables in its JSON body.

Here is a part of that body:

                "@type": "StringValue",
                "name": "content",
                "value": "{{signature}}"

Signature is an environment variable. There is also another block of code with 
{{portrait}} as a variable. Both have values in "current" column in the environment.

Request works fine from Postman collection runner. But when I use newman for the same 
request - signature variable doesn't get populated. In the request body I get: ```"value": ""
Portrait variable gets populated.

Why is this so? The only way I got it to work was to copy the signature variable value into
"initial" column as well. Why did it made a difference?