Why does the setter run twice per instance

Ouput

$ python whySetterMultipleTimes.py
<PyQt5.QtQml.QJSValue object at 0x7efd3eb4a978>
objectName:  customType
names:  ['one', 'two']
Times in setter:  1

<PyQt5.QtQml.QJSValue object at 0x7efd3eb4a978>
objectName:  customType2
names:  ['one', 'two']
Times in setter:  1

<PyQt5.QtQml.QJSValue object at 0x7efd3eb4a978>
objectName:  customType
names:  ['one', 'two']
Times in setter:  2
<PyQt5.QtQml.QJSValue object at 0x7efd3eb4a9e8>
objectName:  customType2
names:  ['one', 'two']
Times in setter:  2


$

whySetterMultipleTimes.py

import sys

from PyQt5 import QtCore, QtQml
from PyQt5.QtWidgets import QApplication


class CustomType(QtCore.QObject):
    names_changed = QtCore.pyqtSignal()
    def __init__(self, parent = None):
        super().__init__(parent)

        self._names = []
        self._times_in_setter = 0

    #@QtCore.pyqtProperty(QtQml.QJSValue, notify = names_changed)
    #@QtCore.pyqtProperty(list, notify = names_changed)
    @QtCore.pyqtProperty(QtCore.QVariant, notify = names_changed)
    def names(self):
        return self._names
    @names.setter
    def names(self, names):
        print(names)
        self._times_in_setter += 1
        names_list = names.toVariant()
        # if names_list == self._names:
        #     return
        self._names = names_list
        print("objectName: ", self.objectName())
        print("names: ", self._names)
        print("Times in setter: ", self._times_in_setter)
        self.names_changed.emit()
        print()


QML = b"""
import QtQuick 2.7
import QtQuick.Controls 1.4

import CustomType 1.0

ApplicationWindow {
    visible: true
    width: 800
    height: 600

    Column {
        ComboBox {
            model: customType.names
        }
        ComboBox {
            model: customType2.names
        }
    }

    CustomType {
      id: customType
      objectName: "customType"
      names: ["one", "two"]
    }
    CustomType {
      id: customType2
      objectName: "customType2"
      names: customType.names
   }
}
"""

app = QApplication(sys.argv)
QtQml.qmlRegisterType(CustomType, 'CustomType', 1, 0, 'CustomType')
engine = QtQml.QQmlApplicationEngine()
engine.loadData(QML)
app.exec_()