Abnormal Behaviour of the Zoom In and Zoom Out Functionality of the JFreeChart?

Your example appears to be mixing the two approaches suggested here, invoking the chart panel's handler from within your own actionPerformed() implementation. While the chart panel handlers are reusable, they are not re-entrant. Instead, use the chart panel's implementation directly. The example below focuses on two buttons to zoom the domain in and out:

toolBar.add(createButton("Zoom In X", ZOOM_IN_DOMAIN_COMMAND));
toolBar.add(createButton("Zoom Out X", ZOOM_OUT_DOMAIN_COMMAND));
…
private JButton createButton(String name, String command) {
    final JButton b = new JButton(name);
    b.setActionCommand(command);
    b.addActionListener(chartPanel);
    return b;
}

After clicking Zoom In X:

After clicking Zoom Out X:

This complete example re-factors the createButton() method to exercise the available zoom handlers and illustrates using a JToolBar.

import java.awt.BorderLayout;
import java.awt.EventQueue;
import java.text.NumberFormat;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JToolBar;
import org.jfree.chart.ChartFactory;
import org.jfree.chart.ChartPanel;
import org.jfree.chart.JFreeChart;
import org.jfree.chart.axis.NumberAxis;
import org.jfree.chart.plot.XYPlot;
import org.jfree.chart.renderer.xy.XYLineAndShapeRenderer;
import org.jfree.data.time.TimeSeries;
import org.jfree.data.time.TimeSeriesCollection;
import org.jfree.data.time.Year;
import org.jfree.data.xy.XYDataset;
import static org.jfree.chart.ChartPanel.*;

/** @see https://stackoverflow.com/a/41337259/230513 */
public class ZoomDemo {

    private static final String TITLE = "Return On Investment";
    private final ChartPanel chartPanel = createChart();

    public ZoomDemo() {
        JFrame f = new JFrame(TITLE);
        f.setTitle(TITLE);
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.setLayout(new BorderLayout(0, 5));
        f.add(chartPanel, BorderLayout.CENTER);
        chartPanel.setMouseWheelEnabled(true);

        JPanel panel = new JPanel();
        JToolBar toolBar = new JToolBar();
        toolBar.add(createButton("Zoom In", ZOOM_IN_BOTH_COMMAND));
        toolBar.add(createButton("Zoom In X", ZOOM_IN_DOMAIN_COMMAND));
        toolBar.add(createButton("Zoom In Y", ZOOM_IN_RANGE_COMMAND));
        toolBar.add(createButton("Zoom Out", ZOOM_OUT_BOTH_COMMAND));
        toolBar.add(createButton("Zoom Out X", ZOOM_OUT_DOMAIN_COMMAND));
        toolBar.add(createButton("Zoom Out Y", ZOOM_OUT_RANGE_COMMAND));
        toolBar.add(createButton("Reset", ZOOM_RESET_BOTH_COMMAND));
        toolBar.add(createButton("Reset X", ZOOM_RESET_DOMAIN_COMMAND));
        toolBar.add(createButton("Reset Y", ZOOM_RESET_RANGE_COMMAND));
        panel.add(toolBar);
        f.add(panel, BorderLayout.SOUTH);
        f.pack();
        f.setLocationRelativeTo(null);
        f.setVisible(true);
    }

    private JButton createButton(String name, String command) {
        final JButton b = new JButton(name);
        b.setActionCommand(command);
        b.addActionListener(chartPanel);
        return b;
    }

    private ChartPanel createChart() {
        XYDataset roiData = createDataset();
        JFreeChart chart = ChartFactory.createTimeSeriesChart(
            TITLE, "Date", "Value", roiData, true, true, false);
        XYPlot plot = chart.getXYPlot();
        XYLineAndShapeRenderer renderer =
            (XYLineAndShapeRenderer) plot.getRenderer();
        renderer.setBaseShapesVisible(true);
        NumberFormat currency = NumberFormat.getCurrencyInstance();
        currency.setMaximumFractionDigits(0);
        NumberAxis rangeAxis = (NumberAxis) plot.getRangeAxis();
        rangeAxis.setNumberFormatOverride(currency);
        return new ChartPanel(chart);
    }

    private XYDataset createDataset() {
        TimeSeriesCollection tsc = new TimeSeriesCollection();
        tsc.addSeries(createSeries("Projected", 200));
        tsc.addSeries(createSeries("Actual", 100));
        return tsc;
    }

    private TimeSeries createSeries(String name, double scale) {
        TimeSeries series = new TimeSeries(name);
        for (int i = 0; i < 6; i++) {
            series.add(new Year(2016 + i), Math.pow(2, i) * scale);
        }
        return series;
    }

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {

            @Override
            public void run() {
                ZoomDemo cpd = new ZoomDemo();
            }
        });
    }
}