Fixes updating username on rooms only if setting a new username;

client/views/username/username.coffee

@@ -41,6 +41,8 @@ Template.username.events
 					username.error = true
 				username.username = value
 
-			Meteor.call 'joinDefaultChannels', ->
-				RocketChat.Button.reset(button)
-				instance.username.set(username)
+			RocketChat.Button.reset(button)
+			instance.username.set(username)
+
+			if not err?
+				Meteor.call 'joinDefaultChannels'

packages/rocketchat-lib/package.js

@@ -25,7 +25,7 @@ Package.onUse(function(api) {
 	], ['server']);
 	
 	api.addFiles([
-		'server/methods/joinDefaultChannels.coffee'
+		'server/methods/joinDefaultChannels.coffee',
 		'server/methods/setUsername.coffee'
 	], ['server']);
 

packages/rocketchat-lib/server/functions/setUsername.coffee

@@ -16,20 +16,21 @@ RocketChat.setUsername = (user, username) ->
 
 	previousUsername = user.username
 
-	# Username is available, set username and update all references
-	ChatMessage.update { "u._id": user._id }, { $set: { "u.username": username } }, { multi: true }
+	# Username is available; if coming from old username, update all references
+	if previousUsername
+		ChatMessage.update { "u._id": user._id }, { $set: { "u.username": username } }, { multi: true }
 	
-	# @TODO: update chatmessage mentions
-	ChatMessage.find({ "mentions.username": previousUsername }).forEach (msg) ->
-		updatedMsg = msg.msg.replace(new RegExp("@#{previousUsername}", "ig"), "@#{username}")
-		ChatMessage.update { _id: msg._id, "mentions.username": previousUsername }, { $set: { "mentions.$.username": username, "msg": updatedMsg } }
+		ChatMessage.find({ "mentions.username": previousUsername }).forEach (msg) ->
+			updatedMsg = msg.msg.replace(new RegExp("@#{previousUsername}", "ig"), "@#{username}")
+			ChatMessage.update { _id: msg._id, "mentions.username": previousUsername }, { $set: { "mentions.$.username": username, "msg": updatedMsg } }
 
-	ChatRoom.update { usernames: previousUsername }, { $set: { "usernames.$": username } }, { multi: true }
-	ChatRoom.update { "u._id": user._id }, { $set: { "u.username": username } }, { multi: true }
+		ChatRoom.update { usernames: previousUsername }, { $set: { "usernames.$": username } }, { multi: true }
+		ChatRoom.update { "u._id": user._id }, { $set: { "u.username": username } }, { multi: true }
 
-	ChatSubscription.update { "u._id": user._id }, { $set: { "u.username": username } }, { multi: true }
-	ChatSubscription.update { name: previousUsername, t: "d" }, { $set: { name: username } }, { multi: true }
+		ChatSubscription.update { "u._id": user._id }, { $set: { "u.username": username } }, { multi: true }
+		ChatSubscription.update { name: previousUsername, t: "d" }, { $set: { name: username } }, { multi: true }
 
+	# Set new username
 	Meteor.users.update { _id: user._id }, { $set: { username: username } }
 	user.username = username
 	return user