QtCreator 3.6.0, Debian Stretch, Mate DE.
1) Create plain C++ project (console program, code don't mater).
2) Select debug build.
3) Run program via F5 (with debugger). After this QtCreator open terminal window. But after a split second terminal lost focus, and QtCreator become active window.
4) Run program via ctrl+R (without debugger). No problem, terminal become active window.

I'm don't think this is correct behavior. Of course, if program stopped in break point, QtCreator must get focus. But this is other case.