Index: src/org/openstreetmap/josm/actions/mapmode/ExtrudeAction.java
===================================================================
--- src/org/openstreetmap/josm/actions/mapmode/ExtrudeAction.java	(revision 7224)
+++ src/org/openstreetmap/josm/actions/mapmode/ExtrudeAction.java	(working copy)
@@ -178,6 +178,8 @@
     private boolean dualAlignActive;
     /** Dual alignment reference segments */
     private ReferenceSegment dualAlignSegment1, dualAlignSegment2;
+    /** {@code true}, if new segment was collapsed */
+    private boolean dualAlignSegmentCollapsed;
     // Dual alignment UI stuff
     private final DualAlignChangeAction dualAlignChangeAction;
     private final JCheckBoxMenuItem dualAlignCheckboxMenuItem;
@@ -264,8 +266,12 @@
                 Main.warn("Extrude: unknown mode " + mode);
                 rv = new StringBuilder();
             }
-            if (dualAlignActive)
+            if (dualAlignActive) {
                 rv.append(" ").append(tr("Dual alignment active."));
+                if (dualAlignSegmentCollapsed) {
+                    rv.append(" ").append(tr("Segment collapsed due to its direction reversing."));
+                }
+            }
         }
         return rv.toString();
     }
@@ -390,6 +396,7 @@
             // Otherwise switch to another mode
             if (dualAlignEnabled && checkDualAlignConditions()) {
                 dualAlignActive = true;
+                dualAlignSegmentCollapsed = false;
                 calculatePossibleDirectionsForDualAlign();
             } else {
                 dualAlignActive = false;
@@ -894,6 +901,9 @@
                 EastNorth collapsedSegmentPosition = Geometry.getLineLineIntersection(dualAlignSegment1.p1, dualAlignSegment1.p2, dualAlignSegment2.p1, dualAlignSegment2.p2);
                 newN1en = collapsedSegmentPosition;
                 newN2en = collapsedSegmentPosition;
+                dualAlignSegmentCollapsed = true;
+            } else {
+                dualAlignSegmentCollapsed = false;
             }
         } else {
             newN1en = n1movedEn;