Windows IME disabled by clicking MDI title bar

On Windows (Windows 10 in my case), add Japanese as an input language.

Build and run the MDI example (qt/qtbase/examples/widgets/mainwindows/mdi).

Using the language icon in the Windows task bar, select Japanese as the input language. This displays a J icon in the task bar with a script icon to the left which shows either A for Romaji or the Japanese character for Hiragana.

In the MDI example program, choose File->New to create a new MDI child window.

Click the title bar of the MDI child window. Look in the task bar, to the left of the J icon and note that the icon to the left of the J icon now shows as X, indicating that IME is disabled. This is wrong because the MDI client area still has the focus, as indicated by the blinking cursor.

Click the body of the MDI child window. Note that the icon to the left of the J icon is now correct (either A or Hiragana).

In summary, clicking the title bar of an MDI child disables IME but it should remain enabled or disabled, following the Qt::WA_InputMethodEnabled attribute of the client QWidget.