Plan variables don't seem to make it to deployment projects reliably

I have a number of projects which I deploy to multiple AWS environments. The deployment process is identical, save for which environment it goes to, and project-specific details.

As such, I put the project-specific details into the Bamboo build plan as variables, and the environment-specific details into the deployment environment as variables. The tasks then are "cut-and-paste" for uniformity.

This all works great when I create a release from builds that I triggered manually in Bamboo. However, when I create a release from an automatically triggered build, these custom plan variables aren't passed down.