Index: /trunk/src/org/openstreetmap/josm/data/vector/VectorPrimitive.java
===================================================================
--- /trunk/src/org/openstreetmap/josm/data/vector/VectorPrimitive.java	(revision 18519)
+++ /trunk/src/org/openstreetmap/josm/data/vector/VectorPrimitive.java	(revision 18520)
@@ -45,4 +45,6 @@
             }
         }
+        updateFlags(FLAG_TAGGED, hasKeys() && keys()
+                .anyMatch(key -> !isUninterestingKey(key)));
     }
 
@@ -59,5 +61,5 @@
     @Override
     public boolean isTagged() {
-        return !this.getInterestingTags().isEmpty();
+        return (flags & FLAG_TAGGED) != 0;
     }