Index: trunk/src/org/openstreetmap/josm/data/osm/OsmPrimitive.java
===================================================================
--- trunk/src/org/openstreetmap/josm/data/osm/OsmPrimitive.java	(revision 11290)
+++ trunk/src/org/openstreetmap/josm/data/osm/OsmPrimitive.java	(revision 11291)
@@ -686,5 +686,5 @@
             l.addAll(getDiscardableKeys());
             l.addAll(getWorkInProgressKeys());
-            uninteresting = Main.pref.getCollection("tags.uninteresting", l);
+            uninteresting = new HashSet<>(Main.pref.getCollection("tags.uninteresting", l));
         }
         return uninteresting;
@@ -698,5 +698,5 @@
     public static Collection<String> getDiscardableKeys() {
         if (discardable == null) {
-            discardable = Main.pref.getCollection("tags.discardable",
+            discardable = new HashSet<>(Main.pref.getCollection("tags.discardable",
                     Arrays.asList(
                             "created_by",
@@ -743,5 +743,5 @@
                             "yh:WIDTH",
                             "yh:WIDTH_RANK"
-                        ));
+                        )));
         }
         return discardable;
@@ -756,6 +756,6 @@
     public static Collection<String> getWorkInProgressKeys() {
         if (workinprogress == null) {
-            workinprogress = Main.pref.getCollection("tags.workinprogress",
-                    Arrays.asList("note", "fixme", "FIXME"));
+            workinprogress = new HashSet<>(Main.pref.getCollection("tags.workinprogress",
+                    Arrays.asList("note", "fixme", "FIXME")));
         }
         return workinprogress;