This is about spring-boot-loader module and org.springframework.boot.loader.launch package and is currently in the master Git branch.

The JarLauncher is written in a way that it can be used on the unpacked JARs (used in a layered Docker images) easily, because it reads the existing BOOT-INF/classpath.idx and thus respects the order of libraries. The PropertiesLauncher does not read the classpath.idx nor have an option to specify it, so the expected order of libraries is not respected. There is a possibility to read the index by script and put it into the loader.path system property, but that would be large to specify it via the command line, so this brings another complication (although solvable). Conclusion is that the PropertiesLauncher cannot be used easily on the unpacked JARs - on the layered images.