Index: trunk/src/org/openstreetmap/josm/actions/mapmode/SelectAction.java
===================================================================
--- trunk/src/org/openstreetmap/josm/actions/mapmode/SelectAction.java	(revision 1711)
+++ trunk/src/org/openstreetmap/josm/actions/mapmode/SelectAction.java	(revision 1712)
@@ -17,4 +17,5 @@
 import java.util.LinkedList;
 import java.util.List;
+import java.util.TreeSet;
 
 import javax.swing.JOptionPane;
@@ -36,4 +37,5 @@
 import org.openstreetmap.josm.data.osm.visitor.AllNodesVisitor;
 import org.openstreetmap.josm.data.osm.visitor.SimplePaintVisitor;
+import org.openstreetmap.josm.gui.ExtendedDialog;
 import org.openstreetmap.josm.gui.MapFrame;
 import org.openstreetmap.josm.gui.MapView;
@@ -417,4 +419,29 @@
             } else {
                 Collection<OsmPrimitive> selection = Main.ds.getSelected();
+                Collection<OsmPrimitive> s = new TreeSet<OsmPrimitive>();
+                int max = Main.pref.getInteger("warn.move.maxelements", 20);
+                for (OsmPrimitive osm : selection)
+                {
+                    if(osm instanceof Node)
+                        s.add(osm);
+                    else if(osm instanceof Way)
+                    {
+                        s.add(osm);
+                        s.addAll(((Way)osm).nodes);
+                    }
+                    if(s.size() > max)
+                    {
+                        if(1 != new ExtendedDialog(Main.parent, tr("Move elements"),
+                        tr("You did move more than {0} elements. "
+                        + "Moving a large number of elements is often an error.\n"
+                        + "Really move them?", max),
+                        new String[] {tr("Move them"), tr("Undo move")},
+                        new String[] {"reorder.png", "cancel.png"}).getValue())
+                        {
+                            Main.main.undoRedo.undo();
+                        }
+                        break;
+                    }
+                }
                 if (ctrl) {
                     Collection<Node> affectedNodes = AllNodesVisitor.getAllNodes(selection);