That's strange, because when moving diagonally, I still get hit often, seemingly at random. Or when trying to switch directions going side to side, I'm not sure if the few-frame grace period is there, because even instantly switching from left to right and making sure to not press both keys at once still causes damage. The only way I've been able to safely change direction is if I start moving up or down first, then change direction, but it does seem moving in a square-like pattern is more often than not enough to dodge the attack safely.