diff --git a/chrome/content/zotero/xpcom/commons.js b/chrome/content/zotero/xpcom/commons.js
index 28f8130c1..bfdcc84b0 100644
--- a/chrome/content/zotero/xpcom/commons.js
+++ b/chrome/content/zotero/xpcom/commons.js
@@ -119,8 +119,8 @@ Zotero.Commons = new function() {
 
 					// newPrefBucketNames currently contains intersection
 					// of prefBucketNames and iaBucketNames
-					var askToAddBuckets = zu.arrayDiff(newPrefBucketNames, iaBucketNames);
-					var askToRemoveBuckets = zu.arrayDiff(newPrefBucketNames, prefBucketNames);
+					var askToAddBuckets = zu.arrayDiff(iaBucketNames, newPrefBucketNames);
+					var askToRemoveBuckets = zu.arrayDiff(prefBucketNames, newPrefBucketNames);
 
 					// prompt user about adding buckets
 					for(var i = 0, len = askToAddBuckets.length; i < len; i++) {
diff --git a/chrome/content/zotero/xpcom/data/collection.js b/chrome/content/zotero/xpcom/data/collection.js
index ee7cb73f3..53e5ae437 100644
--- a/chrome/content/zotero/xpcom/data/collection.js
+++ b/chrome/content/zotero/xpcom/data/collection.js
@@ -820,16 +820,16 @@ Zotero.Collection.prototype.diff = function (collection, includeMatches, ignoreO
 	
 	// For the moment, just compare children and increase numDiffs if any differences
 	var d1 = Zotero.Utilities.prototype.arrayDiff(
-		otherData.childCollections, thisData.childCollections
-	);
-	var d2 = Zotero.Utilities.prototype.arrayDiff(
 		thisData.childCollections, otherData.childCollections
 	);
+	var d2 = Zotero.Utilities.prototype.arrayDiff(
+		otherData.childCollections, thisData.childCollections
+	);
 	var d3 = Zotero.Utilities.prototype.arrayDiff(
-		otherData.childItems, thisData.childItems
+		thisData.childItems, otherData.childItems
 	);
 	var d4 = Zotero.Utilities.prototype.arrayDiff(
-		thisData.childItems, otherData.childItems
+		otherData.childItems, thisData.childItems
 	);
 	numDiffs += d1.length + d2.length;
 	
diff --git a/chrome/content/zotero/xpcom/data/tag.js b/chrome/content/zotero/xpcom/data/tag.js
index 0fb4d8fef..951124ff0 100644
--- a/chrome/content/zotero/xpcom/data/tag.js
+++ b/chrome/content/zotero/xpcom/data/tag.js
@@ -369,8 +369,8 @@ Zotero.Tag.prototype.save = function (full) {
 				var sql = "SELECT itemID FROM itemTags WHERE tagID=?";
 				var dbItemIDs = Zotero.DB.columnQuery(sql, tagID);
 				if (dbItemIDs) {
-					removed = Zotero.Utilities.prototype.arrayDiff(currentIDs, dbItemIDs);
-					newids = Zotero.Utilities.prototype.arrayDiff(dbItemIDs, currentIDs);
+					removed = Zotero.Utilities.prototype.arrayDiff(dbItemIDs, currentIDs);
+					newids = Zotero.Utilities.prototype.arrayDiff(currentIDs, dbItemIDs);
 				}
 				else {
 					newids = currentIDs;
@@ -379,10 +379,10 @@ Zotero.Tag.prototype.save = function (full) {
 			else {
 				if (this._previousData.linkedItems) {
 					removed = Zotero.Utilities.prototype.arrayDiff(
-						currentIDs, this._previousData.linkedItems
+						this._previousData.linkedItems, currentIDs
 					);
 					newids = Zotero.Utilities.prototype.arrayDiff(
-						this._previousData.linkedItems, currentIDs
+						currentIDs, this._previousData.linkedItems
 					);
 				}
 				else {
@@ -471,10 +471,10 @@ Zotero.Tag.prototype.diff = function (tag, includeMatches, ignoreOnlyDateModifie
 	
 	// For the moment, just compare linked items and increase numDiffs if any differences
 	var d1 = Zotero.Utilities.prototype.arrayDiff(
-		thisData.linkedItems, otherData.linkedItems
+		otherData.linkedItems, thisData.linkedItems
 	);
 	var d2 = Zotero.Utilities.prototype.arrayDiff(
-		otherData.linkedItems, thisData.linkedItems
+		thisData.linkedItems, otherData.linkedItems
 	);
 	numDiffs += d1.length + d2.length;
 	
diff --git a/chrome/content/zotero/xpcom/sync.js b/chrome/content/zotero/xpcom/sync.js
index 72ab580bf..6eaca2b51 100644
--- a/chrome/content/zotero/xpcom/sync.js
+++ b/chrome/content/zotero/xpcom/sync.js
@@ -2989,7 +2989,7 @@ Zotero.Sync.Server.Data = new function() {
 		if (!itemIDs) {
 			return false;
 		}
-		var newItemIDs = Zotero.Utilities.prototype.arrayDiff(childItems, itemIDs);
+		var newItemIDs = Zotero.Utilities.prototype.arrayDiff(itemIDs, childItems);
 		if (itemIDs.length == newItemIDs.length) {
 			return false;
 		}
diff --git a/chrome/content/zotero/xpcom/utilities.js b/chrome/content/zotero/xpcom/utilities.js
index 65dd401af..a52286088 100644
--- a/chrome/content/zotero/xpcom/utilities.js
+++ b/chrome/content/zotero/xpcom/utilities.js
@@ -366,10 +366,10 @@ Zotero.Utilities.prototype.isEmpty = function (obj) {
  * Compares an array with another and returns an array with
  *	the values from array2 that don't exist in array1
  *
- * @param	{Array}		array1			Array that will be checked
- * @param	{Array}		array2			Array that will be compared
+ * @param	{Array}		array1
+ * @param	{Array}		array2
  * @param	{Boolean}	useIndex		If true, return an array containing just
- *										the index of the comparator's elements;
+ *										the index of array2's elements;
  *										otherwise return the values
  */
 Zotero.Utilities.prototype.arrayDiff = function(array1, array2, useIndex) {
@@ -381,9 +381,9 @@ Zotero.Utilities.prototype.arrayDiff = function(array1, array2, useIndex) {
 	}
 	
 	var val, pos, vals = [];
-	for (var i=0; i<array2.length; i++) {
-		val = array2[i];
-		pos = array1.indexOf(val);
+	for (var i=0; i<array1.length; i++) {
+		val = array1[i];
+		pos = array2.indexOf(val);
 		if (pos == -1) {
 			vals.push(useIndex ? pos : val);
 		}