The bug

MC-260779 is partially fixed, however when you set the wordborder large enough to allow sniffers to sniff out block inside the world border, it will occasionally dig into blocks outside the world border.

Note : This bug is occasionally reproducable, you have to try many times to reproduce this.

How to reproduce

1. Create a Superflat world.
2. Use the following command:

   /worldborder set 20

       3. Summon a sniffer.

       4.The sniffer will sniff outs into the blocks inside the world border.

       5. Found the sniffer can dig into the blocks outside the world border after some try.