This brings up the pencil tool which was selected in the very beginning. Since the Move Viewport tool was already selected before step 3, pressing space and middle mouse button should have no effect

PixiEditor/ViewModels/SubViewModels/Main/IoViewModel.cs

@@ -122,10 +122,14 @@ namespace PixiEditor.ViewModels.SubViewModels.Main
         {
             if (setOn)
             {
-                if(!(Owner.ToolsSubViewModel.ActiveTool is MoveViewportTool))
+                var moveViewportToolIsActive = Owner.ToolsSubViewModel.ActiveTool is MoveViewportTool;
+                if (!moveViewportToolIsActive)
+                {
                     Owner.ToolsSubViewModel.SetActiveTool<MoveViewportTool>();
+                    Owner.ToolsSubViewModel.MoveToolIsTransient = true;
+                }
             }
-            else if (Owner.ToolsSubViewModel.LastActionTool != null)
+            else if (Owner.ToolsSubViewModel.LastActionTool != null && Owner.ToolsSubViewModel.MoveToolIsTransient)
             {
                 Owner.ToolsSubViewModel.SetActiveTool(Owner.ToolsSubViewModel.LastActionTool);
             }

PixiEditor/ViewModels/SubViewModels/Main/ToolsViewModel.cs

@@ -23,6 +23,8 @@ namespace PixiEditor.ViewModels.SubViewModels.Main
 
         public Tool LastActionTool { get; private set; }
 
+        public bool MoveToolIsTransient { get; set; }
+
         public Cursor ToolCursor
         {
             get => toolCursor;
@@ -82,6 +84,7 @@ namespace PixiEditor.ViewModels.SubViewModels.Main
 
         public void SetActiveTool(Tool tool)
         {
+            MoveToolIsTransient = false;
             if (ActiveTool != null)
             {
                 activeTool.IsActive = false;