Index: trunk/src/org/openstreetmap/josm/actions/mapmode/DrawAction.java
===================================================================
--- trunk/src/org/openstreetmap/josm/actions/mapmode/DrawAction.java	(revision 617)
+++ trunk/src/org/openstreetmap/josm/actions/mapmode/DrawAction.java	(revision 618)
@@ -349,4 +349,10 @@
 	 */
 	private void computeHelperLine() {
+		if (mousePos == null) {
+			// Don't draw the line.
+			currentMouseEastNorth = null;
+			currentBaseNode = null;
+			return;
+		}
 		
 		double distance = -1;