diff --git a/cura/CuraApplication.py b/cura/CuraApplication.py
index 08b81d568c..4b71047dfc 100755
--- a/cura/CuraApplication.py
+++ b/cura/CuraApplication.py
@@ -815,7 +815,6 @@ class CuraApplication(QtApplication):
         qmlRegisterType(QualitySettingsModel, "Cura", 1, 0, "QualitySettingsModel")
         qmlRegisterType(MachineNameValidator, "Cura", 1, 0, "MachineNameValidator")
         qmlRegisterType(UserChangesModel, "Cura", 1, 1, "UserChangesModel")
-        # qmlRegisterSingletonType(ObjectManager, "Cura", 1, 0, "ObjectManager", ObjectManager.createObjectManager)
 
         qmlRegisterSingletonType(ContainerManager, "Cura", 1, 0, "ContainerManager", ContainerManager.createContainerManager)
 
diff --git a/cura/GCodeListDecorator.py b/cura/GCodeListDecorator.py
index 66ecf3beac..5738d0a7f2 100644
--- a/cura/GCodeListDecorator.py
+++ b/cura/GCodeListDecorator.py
@@ -4,7 +4,7 @@ from UM.Scene.SceneNodeDecorator import SceneNodeDecorator
 class GCodeListDecorator(SceneNodeDecorator):
     def __init__(self):
         super().__init__()
-        self._gcode_list = {}  # []
+        self._gcode_list = []
 
     def getGCodeList(self):
         return self._gcode_list
diff --git a/cura/ObjectManager.py b/cura/ObjectManager.py
index 8361e43d71..413f43ed73 100644
--- a/cura/ObjectManager.py
+++ b/cura/ObjectManager.py
@@ -11,6 +11,7 @@ from PyQt5.QtWidgets import QApplication
 from UM.Preferences import Preferences
 
 
+##  Keep track of all objects in the project
 class ObjectManager(ListModel):
     def __init__(self):
         super().__init__()
diff --git a/cura/Scene/BuildPlateDecorator.py b/cura/Scene/BuildPlateDecorator.py
index 6b4dcfc970..cfbe792699 100644
--- a/cura/Scene/BuildPlateDecorator.py
+++ b/cura/Scene/BuildPlateDecorator.py
@@ -3,6 +3,7 @@ from UM.Application import Application
 from UM.Logger import Logger
 
 
+##  Make a SceneNode build plate aware CuraSceneNode objects all have this decorator.
 class BuildPlateDecorator(SceneNodeDecorator):
     def __init__(self, build_plate_number = -1):
         super().__init__()
diff --git a/plugins/CuraEngineBackend/CuraEngineBackend.py b/plugins/CuraEngineBackend/CuraEngineBackend.py
index c250b9019c..b0f44e931d 100755
--- a/plugins/CuraEngineBackend/CuraEngineBackend.py
+++ b/plugins/CuraEngineBackend/CuraEngineBackend.py
@@ -112,7 +112,6 @@ class CuraEngineBackend(QObject, Backend):
         self._tool_active = False  # If a tool is active, some tasks do not have to do anything
         self._always_restart = True  # Always restart the engine when starting a new slice. Don't keep the process running. TODO: Fix engine statelessness.
         self._process_layers_job = None  # The currently active job to process layers, or None if it is not processing layers.
-        # self._need_slicing = False
         self._build_plates_to_be_sliced = []  # what needs slicing?
         self._engine_is_fresh = True  # Is the newly started engine used before or not?
 
@@ -446,11 +445,6 @@ class CuraEngineBackend(QObject, Backend):
 
         self._invokeSlice()
 
-        # #self.needsSlicing()
-        # self.stopSlicing()
-        # #self._onChanged()
-        # self._invokeSlice()
-
     ##  Called when an error occurs in the socket connection towards the engine.
     #
     #   \param error The exception that occurred.
@@ -476,12 +470,9 @@ class CuraEngineBackend(QObject, Backend):
                     node.getParent().removeChild(node)
 
     def markSliceAll(self):
-        if 0 not in self._build_plates_to_be_sliced:
-            self._build_plates_to_be_sliced.append(0)
-        if 1 not in self._build_plates_to_be_sliced:
-            self._build_plates_to_be_sliced.append(1)
-        if 2 not in self._build_plates_to_be_sliced:
-            self._build_plates_to_be_sliced.append(2)
+        for build_plate_number in range(Application.getInstance().getBuildPlateModel().maxBuildPlate + 1):
+            if build_plate_number not in self._build_plates_to_be_sliced:
+                self._build_plates_to_be_sliced.append(build_plate_number)
 
     ##  Convenient function: mark everything to slice, emit state and clear layer data
     def needsSlicing(self):
diff --git a/plugins/CuraEngineBackend/ProcessSlicedLayersJob.py b/plugins/CuraEngineBackend/ProcessSlicedLayersJob.py
index 916cc4d914..8da18a066d 100644
--- a/plugins/CuraEngineBackend/ProcessSlicedLayersJob.py
+++ b/plugins/CuraEngineBackend/ProcessSlicedLayersJob.py
@@ -84,17 +84,6 @@ class ProcessSlicedLayersJob(Job):
         new_node = SceneNode()
         new_node.addDecorator(BuildPlateDecorator(self._build_plate_number))
 
-        # ## Remove old layer data (if any)
-        # for node in DepthFirstIterator(self._scene.getRoot()):
-        #     if node.callDecoration("getLayerData") and node.callDecoration("getBuildPlateNumber") == self._build_plate_number:
-        #         Logger.log("d", "   # Removing: %s", node)
-        #         node.getParent().removeChild(node)
-        #         #break
-        #     if self._abort_requested:
-        #         if self._progress_message:
-        #             self._progress_message.hide()
-        #         return
-
         # Force garbage collection.
         # For some reason, Python has a tendency to keep the layer data
         # in memory longer than needed. Forcing the GC to run here makes