Index: trunk/src/org/openstreetmap/josm/actions/OrthogonalizeAction.java
===================================================================
--- trunk/src/org/openstreetmap/josm/actions/OrthogonalizeAction.java	(revision 5684)
+++ trunk/src/org/openstreetmap/josm/actions/OrthogonalizeAction.java	(revision 5686)
@@ -342,4 +342,7 @@
                     }
                 }
+                for (Node n : cs) {
+                    s.remove(n);
+                }
 
                 final HashMap<Node, Double> nC = (orientation == HORIZONTAL) ? nY : nX;
@@ -358,10 +361,15 @@
                 }
 
+                // At this point, the two heading nodes (if any) are horizontally aligned, i.e. they
+                // have the same y coordinate. So in general we shouldn't find them in a vertical string
+                // of segments. This can still happen in some pathological cases (see #7889). To avoid
+                // both heading nodes collapsing to one point, we simply skip this segment string and
+                // don't touch the node coordinates.
+                if (orientation == VERTICAL && headingNodes.size() == 2 && cs.containsAll(headingNodes)) {
+                    continue;
+                }
+
                 for (Node n : cs) {
                     nC.put(n, average);
-                }
-
-                for (Node n : cs) {
-                    s.remove(n);
                 }
             }