QWebEngineView selectedText() does not respond to triggerPageAction SelectAll

During porting of Sigil away from QtWebKit to QtWebEngine we noticed the following bug:

After properly loading a QWebEngineView with an xhtml page and waiting for loadFinished (okay = true), the following code sequence always returns a null string for selectedText().

m_Preview->triggerPageAction(QWebEnginePage::SelectAll);
m_Preview->selectedText();

If I instead use triggerPageAction(QWebEnginePage::Copy) after the SelectAll, the clipboard shows the expected text properly.

So selectedText() is not properly being set by the SelectAll action.

There are many similar bugs to this in the QTBUG database that seems to have been fixed in 5.10 timeframe but this bug has not or somehow crept back in.