When I control a lot of identical creatures they're stacked together and there is a little box next to them saying how many there are (for example "x8"). Normally when I declare attackers, I can click on that box to attack with the whole stack.

However, if my opponent controls a planeswalker, when I click on the box, it expects me to click on my opponent or the planeswalker to choose which to attack, but when I do, nothing happens, see attached video. So to attack at all if my opponent controls a planeswalker, I have to manually click on each creature, which is very time consuming if I have a lot of them.