Avoozl The second set of items appears if you uncheck "Control + Tab cycles through tabs in recently used order", and it doesn't disappear when you turn it back on. As far as I can tell, they are always greyed out and are not useful for anything.
eirk The shortcuts cmd-alt-left/right and cmd-alt-bracket still work, it's just that the shortcuts should revert back to showing cmd-alt-left/right.