After some more debugging, I'm pretty much convinced that something fishy is going on so I'm taking the liberty to submit a formal issue here, since I'm not getting any relevant answer on StackOverflow.
In addition to the snippets on SO, please find attached the whole Gradle project, for your convenience.
composite-properties.zip
My environment:
- macOS 11.0.1 (Big Sur)
- Spring Boot 2.4.0
$ java -version
openjdk version "15.0.1" 2020-10-20
OpenJDK Runtime Environment (build 15.0.1+9-18)
OpenJDK 64-Bit Server VM (build 15.0.1+9-18, mixed mode, sharing)