With a webengine application, (ie. Simplebrowser)

• open a webapp able to open a file with file explorer (outlook, gmail,... - mail attachment with join for ex). A simple example is http://www.w3schools.com/tags/tryit.asp?filename=tryhtml_input_accept
• Either from this explorer windows or outside the new opened explorer window, simple drag a file into the webapp.

Result:
--> the qtwebengine process is blocked permanently,
--> the only solution is to kill the application /!\