Fleetfingers' every skill bonus doesn't stack with ring and amulet.(Armsmaster, Disarm Trap)
It stacks normaly with gauntlets, belt, boots, helm, cloak, armor, weapon etc.
If you equiped three or more items bonus to disarm or armsmaster, highest bonus will aplly.
(ex : Fleetfingers +8 / Boots of armsmaster +3 / Amulet of armsmaster +12 : Armsmaster gets +12 bonus.
Fleetfingers +8 / Boots of armsmaster +3 / Amulet of armsmaster +9 : Armsmaster gets +11 bonus from fleetfingers and boots.)
This bug still occur even under Greyface's patch.