diff --git a/js/id/core/difference.js b/js/id/core/difference.js
index a5a29cf3a..9c1a80ca5 100644
--- a/js/id/core/difference.js
+++ b/js/id/core/difference.js
@@ -9,9 +9,13 @@
 iD.Difference = function(base, head) {
     var changes = {}, length = 0;
 
+    function changed(h, b) {
+        return !_.isEqual(_.omit(h, 'v'), _.omit(b, 'v'));
+    }
+
     _.each(head.entities, function(h, id) {
         var b = base.entities[id];
-        if (!_.isEqual(h, b)) {
+        if (changed(h, b)) {
             changes[id] = {base: b, head: h};
             length++;
         }
@@ -19,7 +23,7 @@ iD.Difference = function(base, head) {
 
     _.each(base.entities, function(b, id) {
         var h = head.entities[id];
-        if (!changes[id] && !_.isEqual(h, b)) {
+        if (!changes[id] && changed(h, b)) {
             changes[id] = {base: b, head: h};
             length++;
         }
diff --git a/js/id/core/entity.js b/js/id/core/entity.js
index ab6f76bc6..0ec14f70b 100644
--- a/js/id/core/entity.js
+++ b/js/id/core/entity.js
@@ -31,7 +31,7 @@ iD.Entity.id.type = function(id) {
 
 // A function suitable for use as the second argument to d3.selection#data().
 iD.Entity.key = function(entity) {
-    return entity.id;
+    return entity.id + ',' + entity.v;
 };
 
 iD.Entity.prototype = {
@@ -72,7 +72,7 @@ iD.Entity.prototype = {
     },
 
     update: function(attrs) {
-        return iD.Entity(this, attrs);
+        return iD.Entity(this, attrs, {v: 1 + (this.v || 0)});
     },
 
     mergeTags: function(tags) {
diff --git a/js/id/svg/areas.js b/js/id/svg/areas.js
index 7b40b8441..8f94a3f69 100644
--- a/js/id/svg/areas.js
+++ b/js/id/svg/areas.js
@@ -58,25 +58,27 @@ iD.svg.Areas = function(projection) {
         });
 
         function drawPaths(areas, klass, closeWay) {
-            var tagClasses = iD.svg.TagClasses();
-
-            if (klass === 'stroke') {
-                tagClasses.tags(iD.svg.MultipolygonMemberTags(graph));
-            }
-
             var paths = surface.select('.layer-' + klass)
                 .selectAll('path.area')
                 .filter(filter)
                 .data(areas, iD.Entity.key);
 
-            paths.enter()
+            var enter = paths.enter()
                 .append('path')
                 .attr('class', function(d) { return d.type + ' area ' + klass + ' ' + d.id; });
 
+            // Optimization: call simple TagClasses only on enter selection. This
+            // works because iD.Entity.key is defined to include the entity v attribute.
+            if (klass !== 'stroke') {
+                enter.call(iD.svg.TagClasses());
+            } else {
+                paths.call(iD.svg.TagClasses()
+                    .tags(iD.svg.MultipolygonMemberTags(graph)));
+            }
+
             paths
                 .order()
                 .attr('d', function(entity) { return path(entity.asGeoJSON(graph, closeWay)); })
-                .call(tagClasses)
                 .call(iD.svg.MemberClasses(graph));
 
             if (klass === 'fill') paths.call(setPattern);
diff --git a/js/id/svg/lines.js b/js/id/svg/lines.js
index 23a02cedd..789bcb3d7 100644
--- a/js/id/svg/lines.js
+++ b/js/id/svg/lines.js
@@ -50,25 +50,27 @@ iD.svg.Lines = function(projection) {
         lines.sort(waystack);
 
         function drawPaths(klass) {
-            var tagClasses = iD.svg.TagClasses();
-
-            if (klass === 'stroke') {
-                tagClasses.tags(iD.svg.MultipolygonMemberTags(graph));
-            }
-
             var paths = surface.select('.layer-' + klass)
                 .selectAll('path.line')
                 .filter(filter)
                 .data(lines, iD.Entity.key);
 
-            paths.enter()
+            var enter = paths.enter()
                 .append('path')
                 .attr('class', function(d) { return 'way line ' + klass + ' ' + d.id; });
 
+            // Optimization: call simple TagClasses only on enter selection. This
+            // works because iD.Entity.key is defined to include the entity v attribute.
+            if (klass !== 'stroke') {
+                enter.call(iD.svg.TagClasses());
+            } else {
+                paths.call(iD.svg.TagClasses()
+                    .tags(iD.svg.MultipolygonMemberTags(graph)));
+            }
+
             paths
                 .order()
                 .attr('d', path)
-                .call(tagClasses)
                 .call(iD.svg.MemberClasses(graph));
 
             paths.exit()
diff --git a/js/id/svg/tag_classes.js b/js/id/svg/tag_classes.js
index 96b907828..434acc62b 100644
--- a/js/id/svg/tag_classes.js
+++ b/js/id/svg/tag_classes.js
@@ -19,7 +19,7 @@ iD.svg.TagClasses = function() {
             var t = tags(entity);
             for (var k in t) {
                 if (!keys.has(k)) continue;
-                classes += ' tag-' + k + ' ' + 'tag-' + k + '-' + t[k];
+                classes += ' tag-' + k + ' tag-' + k + '-' + t[k];
             }
 
             classes = classes.trim();
diff --git a/test/spec/core/entity.js b/test/spec/core/entity.js
index 8ab310f5d..2190d7125 100644
--- a/test/spec/core/entity.js
+++ b/test/spec/core/entity.js
@@ -61,6 +61,14 @@ describe('iD.Entity', function () {
         it("doesn't copy prototype properties", function () {
             expect(iD.Entity().update({})).not.to.have.ownProperty('update');
         });
+
+        it("sets v to 1 if previously undefined", function() {
+            expect(iD.Entity().update({}).v).to.equal(1);
+        });
+
+        it("increments v", function() {
+            expect(iD.Entity({v: 1}).update({}).v).to.equal(2);
+        });
     });
 
     describe("#mergeTags", function () {