I have the Nurwin's Bamboo Spatula (charm item) from the Mara crafting quest that gives Focused Proficiency (1.1% success). I also have the Cloak of the Master Provisioner which gives Focused Proficiency (1.4% success). When I equip just the cloak I gain 1.4% success. If I equip the spatula while I have my cloak on my stat changes by -0.3%. Another player in crafting actually brought this to my attention by mentioning that when he/she equipped the cloak the success chance only changed by +0.3%, not 1.4%. It seems that when he/she equips both they get 1.4, but when I equip both I get 1.1. Since the items are from 2 different quests, have different values of focused proficiency, and are equippable in different item slots these 2 bonuses should stack, not overwrite each other. I've not checked the rest of my tradeskillers yet to see if it's just provisioner or if the other classes have the same issue.