Bonus armor penetration from llast whisper, Battering blows and Yasuo's ult passive

So, if you have the battering blows mastery and a last whisper item, the bonus armor pen seems to be stacking additively. The mastery gives 7% and the item 45% and if you press C to see your champion stats, you will have 52% bonus armor pen if you have both the mastery and either one of or . So, does it really stack additively or is it some kind of bug?

If you have neither the Battering blows talent or nor any of the above items, your % bonus armor pen stats is obviously 0%

Yasuo's ult buff gives you 50% bonus armor pen but if you ult someone but if you look at your stats, the armor pen tab will not display the 50% buff at all. It will only display your flat pen and your bonus % armor pen from the talent and/or the items if you have any. Why is that? Is it a bug that prevents you from getting the armor pen buff or is it that the hud doesn't display it properly?

And the final and most important, if the %bonus armor pen stacks additively then with Yasuo's ult, the Battering blows talent and a last whisper upgrade you will have 7+45+50=102% bonus armor pen which in effect it is 100% bonus armor pen... What is this? is this for real? i have never tested it in an actual game and when i got into a custom to find out i saw that when you ult the buff isn't displayed on the stat tab but only the items are shown... So... what is actualy happening? Is this for real? Is it possible to get effectively 100% bonus armor pen with the items/masteries and yasuo's ult???

a Rioter comment would be highly appreciated in this one. I would really like to know what actualy happens.