QDialog doesn't get focus on GNOME Shell after opening

When a QDialog is shown with QDialog::exec() it doesn't have focus. you have to use Alt+Tab for it to get focus.
But it only happens when the action was triggered by a keyboard shortcut.
If it was triggered by a mouse click it works as expected.

This is easily reproducible in Qt Creator, when you create a new file/project or start a build while having changed files.

The problem occurs under GNOME 3 and Cinnamon which both use GNOME Shell.
Under KDE, Razor-qt, XFCE, LXDE, Openbox, etc. it works.

Also Qt 4 doesn't have that problem.