Possible bug interaction between Ziggs and Alistar

Hello

I'm not quite sure of what i've seen, but when i landed a q+w combo on ziggs while he was stepping on his w this one did not explode like intended but still getting him away, but stunned by my combo, it happened twice, and the first time i just thought it was a simple fail from me, but i noticed he was stun anyway, while getting eject without exploding his mine.

Sorry for the bad english i'm not a native speaker.