Index: trunk/src/org/openstreetmap/josm/data/osm/QuadBuckets.java
===================================================================
--- trunk/src/org/openstreetmap/josm/data/osm/QuadBuckets.java	(revision 13301)
+++ trunk/src/org/openstreetmap/josm/data/osm/QuadBuckets.java	(revision 13304)
@@ -389,4 +389,5 @@
 
     @Override
+    @SuppressWarnings("ModifyCollectionInEnhancedForLoop")
     public boolean retainAll(Collection<?> objects) {
         for (T o : this) {
@@ -394,4 +395,6 @@
                 continue;
             }
+            // In theory this could cause a ConcurrentModificationException
+            // but we never had such bug report in 8 years (since r2263)
             if (!this.remove(o)) {
                 return false;