Cannot input Chinese characters in QWebEngineView Widget

jjoorrpp

qt 5.8.0 msvc2015 32bit
run on Windows 7

There is a <input> elememt in html page, and QWebEngineView load the page.
Cannot input Chinese characters into the <input> element, although IME has switched to Chinese method.
Copy and paste could make it, but IME couldn't direct input.
How to fix it?

If project uses QWebEngineView as QWidget, and system is Windows7, problem could reproduce.
Windows 10 has no problem.
(Somebody says UML has no problem on qt5.8.0, but I didn't try. My project is based on QWidget. Maybe try it later)

It's easy to reproduce bug by qt's demo: webengine demo browser
Do as below:

browser the default page (qt.io),
click search button on the top right corner of the page,
try input non-English non-Ascii characters.