New tasks don't bind properly. What's wrong?

// Problem: User interaction doesn't provide desired results
// Solution: add interactivity so the user can manage daily tasks

var taskInput = document.getElementById("new-task"); //new-task
var addButton = document.getElementsByTagName("button")[0]; //first button
var incompleteTaskHolder = document.getElementById("incomplete-tasks"); //incomplete-tasks
var completedTasksHolder = document.getElementById("completed-tasks"); //completed-tasks

//New Task List Item
var createNewTaskElement = function(taskString) {
  //Create list item
  var listItem = document.createElement("li");

  //Checkbox input
  var checkBox = document.createElement("input"); //checkbox

  //Label
  var label = document.createElement("label");

  //Input (text)
  var editInput = document.createElement("input"); //text

  //Button.edit
  var editButton = document.createElement("button");

  //Button.delete
  var deleteButton = document.createElement("button");

  //Each element needs modifying

  checkBox.type = "checkbox";
  editInput.type = "text";
  editButton.innerText = "Edit";
  editButton.className = "Edit";
  deleteButton.innerText = "Delete";
  deleteButton.className = "Delete";

  label.innerText = taskString;


  //Each element needs appending
  listItem.appendChild(checkBox);
  listItem.appendChild(label);
  listItem.appendChild(editInput);
  listItem.appendChild(editButton);
  listItem.appendChild(deleteButton);

  return listItem;
}

// Add a new task
var addTask = function () {
  console.log("Add task...");
  //Create a new li with the text from #new-task
  var listItem = createNewTaskElement(taskInput.value);

  //Append list item to incompleteTaskHolder
  incompleteTaskHolder.appendChild(listItem);
  bindTaskEvents(listItem, taskCompleted);

  taskInput.value = "";
}

// Edit an existing task
var editTask = function () {
  console.log("edit task...");

  var listItem = this.parentNode;

  var editInput = listItem.querySelector("input[type=text");
  var label = listItem.querySelector("label");
  var containsClass = listItem.classList.contains("editMode");

  //if class of parent is .edit
  if(containsClass){
    //switch from .editMode
    //Label text becomes inputs value
    label.innerText = editInput.value;
  } else {
    //Switch to .editMode
    //input value becomes labels text
    editInput.value = label.innerText;
  }
  //Toggle .editMode on list item
  listItem.classList.toggle("editMode");
}

// Delete an existing task
var deleteTask = function () {
  console.log("Delete task...");
  var listItem = this.parentNode;
  var ul = listItem.parentNode;

  // Remove parent li from ul
  ul.removeChild(listItem);
}
// Mark a task as complete
var taskCompleted = function () {
  console.log("Complete task...");

  //Append task li to #completed-tasks
  var listItem = this.parentNode;
  completedTasksHolder.appendChild(listItem);
  bindTaskEvents(listItem, taskIncomplete);
}
// Mark task as incomplete
var taskIncomplete = function () {
  console.log("Incomplete task...");

  //Append task li to #uncompleted-tasks
  var listItem = this.parentNode;
  incompleteTaskHolder.appendChild(listItem);
  bindTaskEvents(listItem, taskCompleted);
}

var bindTaskEvents = function (taskListItem, checkBoxEventHandler) {
  console.log("Bind list item events");
  //select taskListItems children
  var checkBox = taskListItem.querySelector("input[type='checkbox']");
  var editButton = taskListItem.querySelector("button.edit");
  var deleteButton = taskListItem.querySelector("button.delete");

  //bind editTask to edit button
  editButton.onclick = editTask;
  //bind deleteTask to delete button
  deleteButton.onclick = deleteTask;
  //bind checkBoxEventHandler to checkbox
  checkBox.onchange = checkBoxEventHandler;
}

var ajaxRequest = function() {
 console.log("AJAX request"); 
}
//Set click handler to addTask button
addButton.addEventListener("click", ajaxRequest);
addButton.addEventListener("click", addTask);

//cycle over incompleteTasksHolder ul list items
for(var i = 0; i < incompleteTaskHolder.children.length; i++){
 //bind events to list item's children (taskCompleted)
  bindTaskEvents(incompleteTaskHolder.children[i], taskCompleted);
}

//cycle over incompleteTasksHolder ul list items
for(var i = 0; i < completedTasksHolder.children.length; i++){
  //bind events to list item's children (taskIncomplete)
  bindTaskEvents(completedTasksHolder.children[i], taskIncomplete);
}