Shortcuts requiring but not specifying Shift fail on Mac

QAction shortcuts of the type Command+! or Command+< (US/Canadian English keymap) or Command+1 (French keymap) that require the Shift modifier but don't specify it explicitly always worked reliably. Qt 5.7.1 introduced a regression for me which causes these shortcuts to fail when the QAction is not attached to a menu in the native menubar.

The workaround versions spelling out the shortcut in keymap-specific keystrokes still work (resp. Command+Shift+1 Command+Shift+ Command+Shift+&).

I have adapted the "menus" example to serve as a demonstrator; it adds a "shortcut test action" to the menubar and/or the context menu:
https://github.com/RJVB/shortcut-test-qt5
By default the action has the Command+< shortcut and is added to the menubar in native mode plus to the context menu. In this configuration the shortcut works for me
Launching the app with either `-no-native-menubar` (use an in-window menubar) and/or with `-no-shortcut-test-in-menubar` (don't add the test action to the menubar) renders the shortcut inoperable for me.
The shortcut can be selected via the `--shortcut` option.

See also bug #57990 .