If a multi-release JAR contains resources with the same name but a different extension, then only one of these resources is picked up. This causes errors with projects using eg. FlatLaf where errors are seen in the code editor while compilation works fine. Files such as FlatLightLaf.properties shadows FlatLightLaf.class.
This seems to be caused by an error in CachingFileManager and ModuleFileManager using the file name and location without extension as a map key to look up multi-release files.
The attached projects demonstrate the issue on classpath and modulepath.