why does the region defined in variable gets replaced by $AWS_DEFAULT_REGION

[t1279k]

In the repository variable I have set up the ecr account url. As you see below the region set is us-east-1

But in the pipline script when I try to invoke the variable $ACCOUNT_URL you can see that the region is replaced with $AWS_DEFAULT_REGION. 

Why is this happening is this expected behaviour? Is there a way to prevent it?