Freeciv

Affects gtk3.22, gtk4 and gtk5 clients, Qt client does not have any keys affecting sound volume.

In this code -

  if (state & GDK_SHIFT_MASK) {
    bool volchange = FALSE;

    switch (keyval) {
    case GDK_KEY_plus:
    case GDK_KEY_KP_Add:
      gui_options.sound_effects_volume += 10;
      volchange = TRUE;
      break;

    case GDK_KEY_minus:
    case GDK_KEY_KP_Subtract:
      gui_options.sound_effects_volume -= 10;
      volchange = TRUE;
      break;

    default:
      break;
    }

    if (volchange) {
      struct option *poption = optset_option_by_name(client_optset,
                                                     "sound_effects_volume");

      gui_options.sound_effects_volume = CLIP(0,
                                              gui_options.sound_effects_volume,
                                              100);
      option_changed(poption);

      return TRUE;
    }
  } else if (!(state & GDK_CONTROL_MASK)) {
    switch (keyval) {
    case GDK_KEY_plus:
    case GDK_KEY_KP_Add:
      zoom_step_up();
      return TRUE;

You can't ever get past the volchange part because the "+" key has the GDK_SHIFT_MASK on by definition - it's (GDK_KEY_equals with GDK_SHIFT_MASK). Since this also eats the key press, it won't get to the Menu entries for zoom that #943 wants to add.

We could drop having "+" and "-" affect sound volume, leaving only the keypad GDK_KEY_KP_Add and GDK_KEY_KP_Subtract to do that. (GDK_KEY_plus with Ctrl/Meta mask) is View menu item Show Stack Size.