[REG Qt 5.7.0 -> Qt 5.8] Menu of ComboBox in Welcome mode does not react to input until/including first mouse click

This looks like a bug in Qt but I couldn't create a minimal example. If you can, please forward the bug to Qt.

1. Install a Qt 5.8 package.
2. Run Creator from this package.
3. Make sure you have at least two Qt versions containing examples configured in "Tools" -> "Options..." -> "Build & Run" -> "Qt versions".
4. Go to Welcome mode, Examples tab.
5. Try to select a different Qt version using the ComboBox.
   The ComboBox' popup menu appears, but then does not do anything until you click on it. This first mouse click is ignored, too. After clicking, it seems to behave correctly.

The ComboBox should be responsive all the time. In Qt 5.7.0, this used to work correctly.