Oh since you are here and this blitzcrank bug is fairly major let me point out a few others.
When you pull a champion across a wall with no space between blitzcrank and the wall the enemy champ pulled stops on the other side of the wall; this started with the new map on SR.
Also other times when you hit a hook after Tristana lands from a rocket jump it considers her taking off not landing so it breaks the hook.
Sometimes the shield from mana barrier when not completely used up but partially used will remain on blitzcrank visually (on the healthbar).
That is all the bugs I as a blitzcrank main can think of right now.
I think he also needs a QoL fix on his Ult passive so that it doesn't aggro neutral monsters in the jungle and drag/baron when they are not already aggro'd. I shouldn't have to use up my ult so I can safely check baron/dragon pit for wards. I also dislike aggro'n every jungle camp I decide to walk past.
If you really wanted to perfect the ult passive on blitzcrank; make it so it doesn't activate on lane minions when blitzcrank is in a bush so that he can safely hide instead of it giving away his position as has happened to me...
Basically his ult passive is more trouble than it is worth but not really cause the damage is kinda insane...