The notes for the 10.5.1.1 beta included:
...which, while something I had requested some far off time ago, I just didn't know about - and think is great (mainly as a boon to ppl here on the forums who want to help others by pointing them to useful options).
But I notice it doesn't work on the Preferences / Folder Tree / Contents page... The controls on that page are evidently ~different than those on other pages as it has the older win95 style dashed selection borders encasing the option you're checking/un-checking... whereas other prefs pages with checkbox controls don't show that - and incidentally work properly with <Ctrl+C>. You also get a tell-tale "ding" sound when trying to <Ctrl+C> items from this page.
If it's something you're inclined to "fix"... I'll re-check the rest of the Prefs pages to look for anything similar. A belated "thanks" again for the feature, quite helpful!