Ziggs magic penetration capped at 40%?

On Ziggs i take piercing thoughts in the ferocity tree which says in the tooltip that it gives me 7% magic penetration. I also, almost every game get Void staff , which says in it's tooltip that it gives 35% magic penetration. However, when i buy void staff and look at my magic penetration i only see 40%. It was to my knowledge that magic penetration percentage capped at 49%. With that said im not sure why it is seeming to cap out at 40% when displayed when it should read as 42%. I challenge anyone to do this and see if they see different.

7+35=42 not 40.

Do i actually have 42% and it is just simply some type of display issue or am i being cheated out of my 2% magic penetration?