qt webchannel is deleted on page reload

The qt object placed in the global Javascript namespace is deleted when the page is reloaded, or a new page is loaded in an existing QWebEngineView.

This is a regression from previous Qt releases (IIRC the last version I tested on was 5.5)

Simply PyQt script to replicate

from PyQt5.Qt import QApplication, QWebEngineView, QTimer, QWebChannel
app = QApplication([])
v = QWebEngineView()
c = QWebChannel()
v.page().setWebChannel(c)
v.setHtml('<script>alert("qt is: " + window.qt)</script>')
v.show()
QTimer.singleShot(1000, v.reload)
app.exec_()

The first alert shows an existing window.qt the second alert (after the reload) show window.qt is undefined.

This breaks communication between the web application and the C++ application using QWebChannel.