when I disassemble my Burglar class item or more, I choose the Legs I want to keep as a scroll, but every time I get the Discretion level Legs.
I repeat in French, because my english is not good enough :
Quand je désassemble un Outil de classe Cambrioleur en choisissant un Leg à récupérer en parchemin, le jeu me donne un parchemin de Niveau de discrétion au lieu du Leg choisi. Impossible d'avoir le parchemin de Leg que je veux...
Popping that phrase into Google translate interprets it as 'Stealth level'. Only legacy that seems fitting is 'sneak movement speed'.
If I understand correctly, OP is trying to deconstruct lvl 100 burglar tools LI that has had at lrast 3 reforges, selects which legacy to extract, but instead always gets this 'stealth level' legacy scroll. Weird issue indeed.
And OP is not good with English so our comments are not likely of much use.
OP would likely fare better by seeking help from other French-speaking players on his/her server...