Blitzcrank not grabbing anyone at the start of the fight: his mana goes empty without spell casting.

Today, I had a problem with in 2 games in a row where he doesn't grab any unit at the start of the fight, and instead, he just walk up to melee range of the enemy front line and start auto attacking, even though I placed Blitz way back, near my bench. So it's not like he was already at melee range, or anything.

And the weirdest part was that his mana bar went empty, while he was walking up there, without him casting anything. His mana was just gone!

This happened quite a few times, in each of those 2 games.

Did anyone experience this, lately?