Veigar's New W's CDR multiplier

im not entirely sure if this is on purpose, but his new W seems to be off. every 50 stacks his W would gain 10% cdr which ends up being multiplicative with his regular CDR. that should be relative to his CD over all while the stack CDR % is separated and shown on his W which it does. As i played the game though, i got 150+ stacks and it gave me 27%, then i got 200 stacks and it showed 34% after getting 250 stacks, it said my W had 41% CDR....shouldve been 50% by that time. Is this a bug or is this how it is really suppose to be? also, in the middle of the game, my W had 3.15sec CD, nothing changed, but when i died the number changed to 3.38seconds. https://cdn.discordapp.com/attachments/360528595317293056/362725175067672576/image.png