Given is an X11 application with a QLineEdit, this application is the only application that runs on an X server (no window manager). If a touch event is now happening on the QLineEdit then it will not receive the input focus. If the same is done using a mouse everything works fine. Dumping all events that are sent to the QLineEdit shows that it only receives events of the type MouseMove, MouseButtonPress¸Paint¸and MouseButtonRelease.

Digging into the code shows that QXcbWindow::handleButtonPressEvent() checks if the current window has the focus and if not calls requestActivate() on it. The same is not done for touch events. A proper place would probably be in QXcbConnection::xi2HandleEvent() in the XI_TouchBegin case.