On my life wizard Grace DreamRider I have Shango's Lifeblade Amulet which gives a +45% lifeblade and the Vibrant Chieftain's Helm which also gives a +45% lifeblade also. However, despite the fact that they come from different gear only one blade is activated if they both are up. Why is it this way? I believe it should be changed so that they are both activated since they come from different gear. Does anyone else agree?
There is no official explanation as to why some things stack and why some don't.
However, based on experience, players have suggested that the item card that is programmed into one item is the same as the item card programmed into another. They have not been programmed to carry any different attributes, such as coming from different card packs, having different stats, or being a "may cast" status. Therefore, in the lack of any different attributes, they will not stack with each other.
Stackable blades/traps fall into different categories. There's Learned, Enchanted, Pet Enchanted, Item Enchanted, TC Enchanted, TC, Pet and Item. All those are stackable. Anything that falls into the same category isn't stackable. You have 2 Items that give the same blade.
I've always assumed each damage modifier spell in the game is tagged by the game code with a unique number. If the modifier activation routine detects a second modifier with the same number as one previously activated by the same spell, it gets ignored and left in place, if the modifier has a code number that hasn't been used yet, it gets activated and used up. Most likely the identifier number is also used to identify the spell that cast it. This why the offensive 70% trap and penalty 30% trap of the feint spell don't stack; they come from the same spell and are tagged with the same code number, so any given attack spell will activate one or the other but not both.