For various ToV necklaces that have the Taelosian Guard click effect, when you click the necklace you get the "You begin casting Taelosian Guard" text, but then it says "Your target does not meet the spell requirements." and the spell doesn't go off / no "Shadow of Memories" buff is cast / no Innate item AA is granted. This is whether or not you have anyone or anything targetted. In contrast some TBL/GMM necklaces with this same click effect work fine. I have seen this on various level 115 characters who can use Prestige items. Items I have personally seen with this trouble: Velium Infused Necklace of Security Gnawed Coldain Neckguard Twisted Sinew Cord On the same characters as above, the following necklace clicks work fine: Free Love Bloodmoon Protection Fetish
Ancient cloak of flames effect if you have it clicked already overrides this buff. So presumably if you had cloak and click telosian buff it wont stack because cloak offers higher haste.
For other clickies, you still get the shadow buff, even if you have clicked a higher level of the item.