Made sure session objects are loaded from the server fresh, no caching.

app/lib/LevelLoader.coffee

@@ -45,7 +45,10 @@ module.exports = class LevelLoader extends CocoClass
       
     @session = new LevelSession()
     @session.url = -> url
-    @session.fetch()
+
+    # Unless you specify cache:false, sometimes the browser will use a cached session
+    # and players will 'lose' code
+    @session.fetch({cache:false})
     @session.once 'sync', @onSessionLoaded, @
     
     if @opponentSessionID

app/lib/surface/SpriteBoss.coffee

@@ -252,7 +252,7 @@ module.exports = class SpriteBoss extends CocoClass
   # Marks
 
   updateSelection: ->
-    if @selectedSprite and (not @selectedSprite.thang.exists or not @world.getThangByID @selectedSprite.thang.id)
+    if @selectedSprite?.thang and (not @selectedSprite.thang.exists or not @world.getThangByID @selectedSprite.thang.id)
       @selectSprite null, null, null
     @updateTarget()
     return unless @selectionMark

app/models/CocoModel.coffee

@@ -81,7 +81,7 @@ class CocoModel extends Backbone.Model
     return super attrs, options
 
   fetch: ->
-    super()
+    super(arguments...)
     @loading = true
 
   markToRevert: ->