Ember calculated property is recalculated without its dependencies changed - ember.js

Question

I have an calculated property(named userFields) depending on another calculated property(named userList). When the object(it's a view) is initialised, I found the property "userFields" was calculated hundreds of times with "userList" calculated only once, according to the console log. I don't know why does this happened.
Here are my codes:
App.MainServiceInfoApplicationQueueUserGroupSelectView = Ember.View.extend({
templateName: require('templates/main/service/info/applicationqueues/user_group_select'),
userCollapse: false,
groupCollapse: false,
toggleUserCollapse: function() {
myview = this;
this.set('userCollapse', !this.get('userCollapse'));
},
toggleGroupCollapse: function() {
this.set('groupCollapse', !this.get('groupCollapse'));
},
userList: function() {
console.log('calc user list'); // This is printed only once
var list = [];
App.User.find().forEach(function(item) {
list.push(item);
});
return list;
}.property('App.User.find()'),
groupList: function() {
var list = [];
App.Resourcegroup.find().forEach(function(item) {
list.push(item);
});
return list;
}.property('App.Resourcegroup.find()'),
userFields: function() {
console.log('calc user fields'); // This is printed hundreds of times
// Parse value
var parsedValues = [];
try {
var usersFromValue = this.get('value').split(' ')[0].split('/');
for (var i = 0; i < usersFromValue.length; i++)
parsedValues.push(usersFromValue[i]);
} catch (e) {}
var fields = [];
for (var i = 0; i < this.get('userList').length; i++) {
var item = this.get('userList')[i];
fields.push(Ember.Object.create({
viewClass: Ember.Checkbox.extend({
value: false,
checkedBinding: 'value'
}),
displayName: item.get('userName'),
name: item.get('userName'),
value: parsedValues.contains(item.get('userName'))
}));
}
return fields;
}.property('userList'),
groupFields: function() {
// Parse value
var parsedValues = [];
try {
var groupsFromValue = this.get('value').split(' ')[1].split('/');
for (var i = 0; i < groupsFromValue.length; i++)
parsedValues.push(groupsFromValue[i]);
} catch (e) {}
var fields = [];
for (var i = 0; i < this.get('groupList').length; i++) {
var item = this.get('groupList')[i];
fields.push(Ember.Object.create({
viewClass: Ember.Checkbox.extend({
value: false,
checkedBinding: 'value'
}),
displayName: item.get('groupName'),
name: item.get('groupName'),
value: parsedValues.contains(item.get('groupName'))
}));
}
return fields;
}.property('groupList'),
users: function() {
console.log('calc users'); // This is printed as many times as 'calc user fields' was printed
var list = [];
for (var i = 0; i < this.get('userFields').length; i++) {
var theField = this.get('userFields')[i];
if (parseBoolean(theField.get('value')) == true) list.push(theField.get('name'));
}
return list;
}.property('userFields, userFields.#each.value'),
groups: function() {
var list = [];
for (var i = 0; i < this.get('groupFields').length; i++) {
var theField = this.get('groupFields')[i];
if (parseBoolean(theField.get('value')) == true) list.push(theField.get('name'));
}
return list;
}.property('groupFields, groupFields.#each.value'),
usersString: function() {
return this.get('users').join(', ');
}.property('users'),
groupsString: function() {
return this.get('groups').join(', ');
}.property('groups'),
usersValue: function() {
return this.get('users').join('/');
}.property('users'),
groupsValue: function() {
return this.get('groups').join('/');
}.property('groups'),
value: function() {
return this.get('usersValue') + " " + this.get('groupsValue');
}.property('usersValue', 'groupsValue')
});