At first, after several attempts of trying, I could not repeat it.
However, I tried again today, and I kept doing the shield attack on an enemy, and every now and then link did do a jump attack.... so I guess it's not a glitch afterall.
Am I too observant or is this game full of glitches?
In city in the sky, when fighting an enemy, I pressed the shield attack button and link did a jump attack instead.
I swear I pushed the right button. 100% certain I did...