Mutant rabbit

They didn't.

Perhaps this is related to the time-travelling characters mentioned in another thread. I mean, if the game "thinks" the task is still on, the rabbits will still be there, but in fact the task has somehow finished early.

I had the same problem last night, but when I stored the Rabbit and took him out of storage the multiples went away.

The funny thing is, I assigned the rabbit to the mutate task and multiple rabbits are still in my town. Well, they don't bother me, so I'll just let them be for now and store it later.