JTable starts editing when F3 is pressed - howto disable?

It behaves differently because it tries to pass key strokes to the editor and overrides processKeyBinding to that end. Try:

import java.awt.EventQueue;
import java.awt.event.KeyEvent;
import java.util.EventObject;

import javax.swing.JFrame;
import javax.swing.JScrollPane;
import javax.swing.JTable;
import javax.swing.table.DefaultTableModel;

public class TestJTable {
    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                JTable table = new JTable(new DefaultTableModel(1, 1)) {
                    @Override
                    public boolean editCellAt(int row, int column, EventObject e) {
                        if (e instanceof KeyEvent) {
                            int code = ((KeyEvent) e).getKeyCode();
                            int start = KeyEvent.VK_F1;
                            int end = KeyEvent.VK_F21;
                            if (code != KeyEvent.VK_F2
                                    && code >= start && code <= end) {
                                return false;
                            }
                        }
                        return super.editCellAt(row, column, e);
                    }
                };
                JFrame frame = new JFrame("Test");
                frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
                frame.getContentPane().add(new JScrollPane(table));
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }
}

Actually JTable does check if the key press triggers an action, but that means it only works if you install the key binding on the table input map with WHEN_ANCESTOR_OF_FOCUSED_COMPONENT.