PMD rule AvoidDuplicateLiterals is not working correctly

[meanmail]

https://hyperskill.org/learn/step/5530#solutions-859202

class CinemaFacadeTestDrive {
    public static void main(String[] args) throws InterruptedException {
        PopcornPopper popcorn = new PopcornPopper();
        Lights lights = new Lights();
        Projector projector = new Projector();

        CinemaFacade cinemaFacade = new CinemaFacade(popcorn, lights, projector);

        cinemaFacade.watchMovie();
        System.out.println("We are watching a movie");
        Thread.sleep(5000);
        System.out.println("The End");
        cinemaFacade.endMovie();
    }
}

class CinemaFacade {
    private PopcornPopper popcorn;
    private Lights lights;
    private Projector projector;

    public CinemaFacade(PopcornPopper popcorn, Lights lights, Projector projector) {
        this.popcorn = popcorn;
        this.lights = lights;
        this.projector = projector;
    }

    public void watchMovie() {
        System.out.println("Get ready to watch a movie...");
        popcorn.on();
        popcorn.pop();
        lights.off();
        projector.on();
    }

    public void endMovie() {
        popcorn.off();
        lights.on();
        projector.off();
    }
}

class PopcornPopper {
    String description = "PopcornPopper";

    public void on() {
        System.out.println(description + " on");
    }

    public void off() {
        System.out.println(description + " off");
    }

    public void pop() {
        System.out.println(description + " popping popcorn!");
    }
}

class Projector {
    String description = "Projector";

    public void on() {
        System.out.println(description + " on");
    }

    public void off() {
        System.out.println(description + " off");
    }
}

class Lights {
    String description = "Lights";

    public void on() {
        System.out.println(description + " on");
    }

    public void off() {
        System.out.println(description + " off");
    }

    public void dim(int level) {
        System.out.println(description + " dimming to " + level + "%");
    }

    public String toString() {
        return description;
    }
}

Style error appears on line System.out.println(description + " off");:
The String " off" appears 3 times in the file

https://pmd.github.io/latest/pmd_rules_java_errorprone.html#avoidduplicateliterals

This rule should work if the string appears 4 or more times (maxDuplicateLiterals = 4) and is more than or equal to 3 characters in length (minimumLength = 3). And in the code, the lines " on" and " off" occur 3 times. But the rule only works on " off". And it shouldn't work. If it should, then why does it not work on the "on" string?

Is there a bug or is everything working correctly?

[GirZ0n]

@meanmail Actually it's not AvoidDuplicateLiterals, but MultipleStringLiterals from Checkstyle. In main this rule has the following properties:

<module name="MultipleStringLiterals">
    <property name="allowedDuplicates" value="2"/>
    <property name="ignoreStringsRegexp" value="^.{1,5}$"/>
</module>

So, all strings of length 5 or less are ignored. But according to the documentation, the regexp for this rule must include quotes, which are not present in the current regexp. That's why Checkstyle ignores " on" (its length including quotes is 5). I'll fix this bug in main-upd.

[meanmail]

@GirZ0n Thank you!