jax bug ??

When I have jax with blue boots and triforce i have 424 ms, when i buy the ms boots enchant (+20ms) I should get 444ms, but I only get 442ms. Same with ninja tabi, doesnt matter which way round I build it. Triforce is plus 8 percent ms, is this taken on current ms, or champions natural ms ? Because if its natural ms then .08 * 350 = 28,

In this order: Jax ms, 350 + blue boots + enchant = 415 Jax ms, 350 + 45 + 20 = 415 (this value is solid) Buy tri force (8percent on natural ms) is + 28ms, so 415 + 28ms = 443

But I only get 442 ms, what am I not understanding here!!!

how does triforce ms 8percent work?!?!?