Senna's unblockable autos

So, i have played Senna for some time now, and i thought she is pretty weak, so i moved back to midlane. I happened to pick Yasuo against Senna on mid (I'm not kidding), and i found out some serious bull*hit going on. Up untill now i though her autos are charging projectiles, but it seems that its laser, ergo as Yasuo or Braum, u can neither block her autos or Q. So i was like, allright, never gonna pick braum against her. But then I found out, that i can block her R with windwall, which in fact, doesn't make much sense, since her R feels like a laser. So i kinda wanted to ask if that is a bug or just a damn weird interaction.
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