It's been 4-5 years, any chance this bug can get addressed? Leads have always had a lot of problem, and if we are going to keep them in the game we might as well fix them.
Lead lines from a mob to a fence post will vanish, leaving only the wrapped lead around the post, and occasionally both will vanish. Eventually the lead will not just be invisible, but gone all together resulting in the mob wandering off. In that case the lead will pop off and remain on the ground as an item until it de-spawns. This is easily produced by tethering a horse to a fence post, flying a few chunks away and back.
In 1.11 (Survival on Server) I'm noticing that creepers rarely run from cats, and skeletons rarely run from dogs. This makes mob farms that use cats/dogs to sort barely work now.
With no path to player, and 2 valid path options (towards cat, or away from cat) it's basically a 50/50 chance of them picking either path.