Marking items as complete works but not always vice versa

var taskInput = document.getElementById("new-task"); //new task
var addButton = document.getElementsByTagName("button")[0]; //firstbutton
var incompleteTasksHolder = document.getElementById("incomplete-tasks");
var completeTasksHolder = document.getElementById("completed-tasks");




//Add new task
var createNewTaskElement = function(taskString) {
  //create LI
  var listItem = document.createElement("li");
    //input checkbox
  var checkbox = document.createElement("input");
    //label
  var label = document.createElement("label");
    //input (text)
  var editInput = document.createElement("input");
    //button.edit
  var editButton = document.createElement("button");
    //button.delete
  var deleteButton = document.createElement("button");

    //Each element needs full text and to be 

  //each element appended

  listItem.appendChild(checkbox);
  listItem.appendChild(label);
  listItem.appendChild(editInput);
  listItem.appendChild(editButton);
  listItem.appendChild(deleteButton);


  return listItem;
}

var addTask = function() {
  console.log("Add");

  //Create new list item with text from #new-task
  var listItem = createNewTaskElement("Some New Task");

  //append LI to inclimpletetaskholder

  incompleteTasksHolder.appendChild(listItem);
  bindTaskEvents(listItem, taskComplete);
}



//Edit exisiting task

var editTask = function() {
    console.log("Edit");
  //When edit button pressed
    //if parent class is .editMode
      //switch from .editmode
      //label become input value
    //else
      //switch to .editmode
      //input value become label

    //toggle .editMode on parent
}


//Delete existing task
var deleteTask = function() {
    console.log("Delete");
   //when delete pressed
    //remove parent li from ul
  var listItem = this.parentNode;
  var ul = listItem.parentNode;
  ul.removeChild(listItem);
}

//Mark tasks complete
var taskComplete = function() {
    console.log("Complete");
  //when checkbox is :checked
  //append task li to #completed-tasks ul
  var listItem = this.parentNode;
  completeTasksHolder.appendChild(listItem);
  bindTaskEvents(listItem, taskComplete);
}

//Mark tasks incomplete
var taskIncomplete = function() {
    console.log("Incomplete");
  //when checkbox unchecked
    //append to incomplete tasks
    var listItem = this.parentNode;
  incompleteTasksHolder.appendChild(listItem);
  bindTaskEvents(listItem, taskIncomplete);
}

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

    //bind delete
  deleteButton.onclick = deleteTask;

    //bind checkbox
  checkBox.onchange = checkBoxEventHandler;
}

//Set click handler to addTask function
addButton.onclick = addTask;

//cycle over incomplete UL LI
for ( var i = 0; i < incompleteTasksHolder.children.length; i++ ) {
  bindTaskEvents(incompleteTasksHolder.children[i], taskComplete);

    //bind events
}


//cycle over complete UL LI
for ( var i = 0; i < completeTasksHolder.children.length; i++ ) {
  bindTaskEvents(completeTasksHolder.children[i], taskIncomplete);

    //bind events
}