Animals bound to fence by lead (rope) suddenly free

I was on the other side of the map, taking home a parrot via boat.
When I came home, I saw that my tethered animals (1 horse, 1 donkey, 4 llamas) just was released from the lead that was attached between them and a fencepost.
The leads(ropes) was laying around on the grass. (See attached photo)

So either something went wrong when the block was loaded, or I got a surprise visit by militant branch of PETA(People for the Ethical Treatment of Animals)?