For example, my issue like the demo browser of qt( create nano browser sample project). Please redirect to http://www.google.com and right click to search text box. The page will reload other than show a context menu.

The other case when i have "<a><img src="pathtoimage"></a>alskdjalsjdkasjd</a>" then you right click serveral times to image then the text. The issue occurs. And many case other when right click to webengineview.

I have built my project with Qt 5.7 it works properly.
Update: It's seem that event mouse right click is not dispatched properly to a link or a button in QWebEngineView. I had tried to capture mouse right-click by re-implement method mousePressEvent before it called to method contextMenuEvent but it's still have the same problem.
Note: i found the problem when right click to button or a link.