please run the following test code:

import javafx.application.Application;
import javafx.scene.*;
import javafx.scene.control.Slider;
import javafx.stage.Stage;
import javafx.geometry.Insets;

public class SliderTest extends Application {

    @Override
    public void start(Stage stage) {

        Group root = new Group();
        Scene scene = new Scene(root, 200, 150);
        stage.setScene(scene);

        Slider s = new Slider(-2., 2., 0.25);
        s.setPadding(new Insets(20, 20, 20, 20));

        s.setShowTickLabels(true);
        s.setShowTickMarks(true);
        s.setMajorTickUnit(0.5);
        s.setMinorTickCount(10);

        root.getChildren().add(s);
        stage.show();
    }

    public static void main(String[] args) { launch(args); }
}

when running with JDK9 b129 (Windows 7), it produces irregular major tick step (1 for the negative values and 0.5 for positive) - please see "scale-nok.png"

no such issue when running with JDK8 b132 on the same machine ("scale-ok.png") - probably a regression?

the behavior for JDK8 looks more reasonable - ignore the ticks if they could not be rendered regularly.