Focus is not always given to the floating dock view

It works fine on Windows, but on Linux, focus is not always given to a floating dock view. Steps to reproduce the bug:

• Run the attached application: a QMainWindow with QTextEdit as central widget and a QLineEdit in a QDockWidget is shown
• Pressing "Ctrl-F" will: show the dock widget, activate it and give the focus to the QLineEdit
• If the dock widget is docked in the main window and hidden, the focus is correctly given to the dock
• If the dock widget is floating and shown, the focus is correctly given to the dock
• If the dock widget is floating and hidden, the focus is not given to the dock