Sion's ult glitch

So the other day when I was playing as , I pressed R to charge bot lane since our tower was under attack. The problem is, when it activated, I kept walking normally, though now had the arrow indicating where I was facing, as if I was in my ult. So I press R again, ult goes on cooldown and I perform the end affect of the ult (the slam). Just wanted to point this out, it only happened the one time though.