This regression is caused by JDK-8183530.

If the visible area of the chart is smaller than the chart itself, the last path is drawn incorrectly.

---------- BEGIN SOURCE ----------
import javafx.application.Application;
import javafx.scene.Group;
import javafx.scene.Scene;
import javafx.scene.chart.AreaChart;
import javafx.scene.chart.NumberAxis;
import javafx.scene.chart.XYChart;
import javafx.stage.Stage;

public class LineAndAreaChartBug extends Application {

    @Override
    public void start(Stage stage) {
        // Define the x-axis upperbound lower than data set
        NumberAxis xAxis = new NumberAxis(1960, 2020, 10);
        xAxis.setLabel("Years");

        // Define the y-axis upperbound lower than data set
        NumberAxis yAxis = new NumberAxis(0, 350, 50);
        yAxis.setLabel("No.of schools");

        AreaChart areaChart = new AreaChart(xAxis, yAxis);
        XYChart.Series series = new XYChart.Series();
        series.setName("No of schools in an year");

        series.getData().add(new XYChart.Data(1970, 15));
        series.getData().add(new XYChart.Data(1980, 30));
        series.getData().add(new XYChart.Data(1990, 60));
        series.getData().add(new XYChart.Data(2000, 120));
        series.getData().add(new XYChart.Data(2000, 160));
        series.getData().add(new XYChart.Data(2013, 240));
        series.getData().add(new XYChart.Data(2014, 300));
        series.getData().add(new XYChart.Data(2030, 300)); // repeat y-value
        series.getData().add(new XYChart.Data(2030, 600));

        areaChart.getData().add(series);
        Group root = new Group(areaChart);
        Scene scene = new Scene(root, 600, 400);
        stage.setTitle("JDK-8183530");
        stage.setScene(scene);
        stage.show();
    }

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