When an animal is tied up with a lead, and the chunk is loaded/unloaded, there is a chance that the lead will break.

This allows the animal to roam free, and the lead to potentially despawn.

THIS IS NOT A DUPLICATE OF https://bugs.mojang.com/browse/MC-14826

I'm sorry for the use of Caps, but having searched for reports on this issue, all those matching the issue I have described have been INCORRECTLY marked as "Duplicates" of the report linked above.
This is NOT the same issue.

In the issue I am reporting, the lead is no longer attached.
In the linked report, the behaviour indicates that the lead is still attached, but is not graphically present.