Unsolved Qt 5.7.1 WebEngineView resizing issue

[xgme]

The WebEngineView widget has a serious resizing issue on CentOS 6. When the main window is resized smaller, the WebEngineView widget does not fill the whole window, which leaves a black gap on top of the main window. The more the main window size is reduced, the wider the black gap.

To reproduce this issue, just build and run webenginewidgets/simplebrowser example on CentOS 6 and reduce the main window size.

Is this a known issue? Any workaround?