Annoying Brad bug T_T!

This is a weird one which I could never figure out.

If you guard both hits, then is guaranteed but + isn't.

If you only guard the second hit, then both and + are guaranteed.

The only way I could attempt to explain it is that it might have something to do with the animation of Sarah during recovery. You notice that her head bobs downwards with the kicking? Well maybe during recovery there's a single frame of animation where Sarah's head is out of the way, causing the + to whiff on the first hit frame, but guarded on the second hit frame since it's no longer guaranteed on frame 15. And this phenomenon of Sarah's head being out of the way is only effective at close range (i.e. when you guard both hits) and not at long range (only guarding the last hit).

I know it's a stretch but I'm at a loss otherwise to explain it.