Mobs often fail climbing down ladders or vines

The bug

Mobs like zombies often fail climbing down ladders or vines. They start climbing down, then apparently try to move forward too early which makes them climb up again. After that they just spin in circles for some time and try to climb down again, see attached video Husk failing to climb down ladder (17w06a).mp4.

How to reproduce

Build a setup as shown in Husk ladder setup (17w06a).png. Make sure the villager is not standing too close the ladders, otherwise the husk will successfully climb down.