What is the nature of this properties file? Is it used as part of the build process or is it used in the product that is produced?
Maven has an extreme dislike for absolute file paths when they're used by Maven itself. Maven was designed in such a way that if you do a "mvn clean" to remove superflous files, zip up the project directory, email it to someone on the other side of the planet, that the unzipped copy should be immediately buildable regardless of what OS or filesystem arrangements the recipient has. All Maven source paths are designed to be located at or below the project directory.
For a properties file used by the product of a Maven build, Maven could not care less where it's located nor whether the path is relative or absolute. That part is left up to whatever application installation process is used.
An IDE is no substitute for an Intelligent Developer.