diff --git a/core/lib/patternlab.js b/core/lib/patternlab.js
index b0c68175f..99accaa15 100644
--- a/core/lib/patternlab.js
+++ b/core/lib/patternlab.js
@@ -1,10 +1,10 @@
 /* 
- * patternlab-node - v2.4.3 - 2016 
+ * patternlab-node - v2.4.4 - 2016 
  * 
  * Brian Muenzenmeyer, Geoff Pursell, and the web community.
- * Licensed under the MIT license.
- *
- * Many thanks to Brad Frost and Dave Olsen for inspiration, encouragement, and advice.
+ * Licensed under the MIT license. 
+ * 
+ * Many thanks to Brad Frost and Dave Olsen for inspiration, encouragement, and advice. 
  *
  */
 
@@ -339,6 +339,7 @@ var patternlab_engine = function (config) {
         patternName: pattern.patternName,
         patternPartial: pattern.patternPartial,
         patternState: pattern.patternState,
+        patternEngineName: pattern.engine.engineName,
         extraOutput: {}
       });
 
@@ -375,17 +376,29 @@ var patternlab_engine = function (config) {
       return getVersion();
     },
     build: function (callback, deletePatternDir) {
+      if (patternlab && patternlab.isBusy) {
+        console.log('Pattern Lab is busy building a previous run - returning early.');
+        return;
+      }
+      patternlab.isBusy = true;
       buildPatterns(deletePatternDir);
       new ui().buildFrontend(patternlab);
       printDebug();
+      patternlab.isBusy = false;
       callback();
     },
     help: function () {
       help();
     },
     patternsonly: function (callback, deletePatternDir) {
+      if (patternlab && patternlab.isBusy) {
+        console.log('Pattern Lab is busy building a previous run - returning early.');
+        return;
+      }
+      patternlab.isBusy = true;
       buildPatterns(deletePatternDir);
       printDebug();
+      patternlab.isBusy = false;
       callback();
     },
     liststarterkits: function () {
diff --git a/core/lib/ui_builder.js b/core/lib/ui_builder.js
index a78240126..4fecf68d8 100644
--- a/core/lib/ui_builder.js
+++ b/core/lib/ui_builder.js
@@ -20,10 +20,6 @@ var ui_builder = function () {
    * @param pattern - the pattern to add
      */
   function addToPatternPaths(patternlab, pattern) {
-    if (!patternlab.patternPaths) {
-      patternlab.patternPaths = {};
-    }
-
     if (!patternlab.patternPaths[pattern.patternGroup]) {
       patternlab.patternPaths[pattern.patternGroup] = {};
     }
@@ -40,10 +36,6 @@ var ui_builder = function () {
    * @param pattern -  the pattern to add
      */
   function addToViewAllPaths(patternlab, pattern) {
-    if (!patternlab.viewAllPaths) {
-      patternlab.viewAllPaths = {};
-    }
-
     if (!patternlab.viewAllPaths[pattern.patternGroup]) {
       patternlab.viewAllPaths[pattern.patternGroup] = {};
     }
@@ -342,10 +334,6 @@ var ui_builder = function () {
       patternGroups: {}
     };
 
-    if (!patternlab.patternTypes) {
-      patternlab.patternTypes = [];
-    }
-
     _.forEach(sortPatterns(patternlab.patterns), function (pattern) {
 
       //ignore patterns we can omit from rendering directly
@@ -560,12 +548,23 @@ var ui_builder = function () {
     writeFile(path.resolve(paths.public.annotations, 'annotations.js'), annotations);
   }
 
+  /**
+   * Reset any global data we use between builds to guard against double adding things
+   */
+  function resetUIBuilderState(patternlab) {
+    patternlab.patternPaths = {};
+    patternlab.viewAllPaths = {};
+    patternlab.patternTypes = [];
+  }
+
   /**
    * The main entry point for ui_builder
    * @param patternlab - global data store
      */
   function buildFrontend(patternlab) {
 
+    resetUIBuilderState(patternlab);
+
     var paths = patternlab.config.paths;
 
     //determine which patterns should be included in the front-end rendering
@@ -626,6 +625,9 @@ var ui_builder = function () {
     },
     groupPatterns: function (patternlab) {
       return groupPatterns(patternlab);
+    },
+    resetUIBuilderState: function (patternlab) {
+      resetUIBuilderState(patternlab);
     }
   };
 
diff --git a/package.json b/package.json
index 25442e032..811086048 100644
--- a/package.json
+++ b/package.json
@@ -1,7 +1,7 @@
 {
   "name": "patternlab-node",
   "description": "Pattern Lab is a collection of tools to help you create atomic design systems. This is the node command line interface (CLI).",
-  "version": "2.4.3",
+  "version": "2.4.4",
   "main": "./core/lib/patternlab.js",
   "dependencies": {
     "diveSync": "^0.3.0",
diff --git a/test/ui_builder_tests.js b/test/ui_builder_tests.js
index 28af58e41..c677fc963 100644
--- a/test/ui_builder_tests.js
+++ b/test/ui_builder_tests.js
@@ -112,6 +112,7 @@ exports['ui_builder'] = {
       new Pattern('patternType1/patternSubType2/grey.mustache'),
       new Pattern('patternType1/patternSubType2/white.mustache')
     );
+    ui.resetUIBuilderState(patternlab);
 
     //act
     var result = ui.groupPatterns(patternlab);
@@ -150,6 +151,7 @@ exports['ui_builder'] = {
       new Pattern('patternType1/patternSubType2/grey.mustache'),
       new Pattern('patternType1/patternSubType2/white.mustache')
     );
+    ui.resetUIBuilderState(patternlab);
 
     //act
     var result = ui.groupPatterns(patternlab);
@@ -179,6 +181,7 @@ exports['ui_builder'] = {
       new Pattern('patternType1/patternSubType2/grey.mustache'),
       new Pattern('patternType1/patternSubType2/white.mustache')
     );
+    ui.resetUIBuilderState(patternlab);
 
     //act
     var result = ui.groupPatterns(patternlab);
@@ -214,6 +217,7 @@ exports['ui_builder'] = {
       new Pattern('patternType1/patternSubType2/grey.mustache'),
       new Pattern('patternType1/patternSubType2/white.mustache')
     );
+    ui.resetUIBuilderState(patternlab);
 
     //act
     var result = ui.groupPatterns(patternlab);
@@ -221,6 +225,25 @@ exports['ui_builder'] = {
     //assert
     test.equals('todo', 'todo');
 
+    test.done();
+  },
+
+  'resetUIBuilderState - reset global objects' : function (test) {
+    //arrange
+    var patternlab = createFakePatternLab({
+      patternPaths: { foo: 1},
+      viewAllPaths: { bar: 2},
+      patternTypes: ['baz']
+    });
+
+    //act
+    ui.resetUIBuilderState(patternlab);
+
+    //assert
+    test.equals(patternlab.patternPaths.foo, undefined);
+    test.equals(patternlab.viewAllPaths.bar, undefined);
+    test.equals(patternlab.patternTypes.length, 0);
+
     test.done();
   }