Surely because there is no timeout when you press the button/shortcut. By the way, it really makes the software slow if you stay on the keys. A little timeout on the function can be interresting.
Same thing happend when we press arrow button for move pixels by pixels an instance on the scene, if you stay on the button all is very slow.
I agree that undo does weird stuff sometimes. I’m always scared when I have to use it
And the undo often scrolls the window, so you can’t keep a close eye on your recent changes to try and spot what was undone.