Sion 90 Degree turns?

So I just lost a pretty important Ranked match due to a sion being able to turn at 90 degrees when using his ult.

I don't think this was intended by riot to happen and he acts like he does it all the time.

If this is not supposed to happen shouldn't this be fixed? It costed us a vital fight and costed us the game. It really sucks to lose a mach to do someone abusing a bug/issue.