There is a chance of about 1 in 5 that an ocelot will just carry on walking around when a lead/leash is attached instead of following you. During that process the lead might extend far beyond the normal length w/o snapping (it will turn invisible though past a certain distance)
Also should be noted the lead can't be attached to a fencepost while the animal AI isn't in "lead" mode.

What I expected:
After attaching a lead, the ocelot would follow me around like a cow or chicken would.
What happened:
Every now and then after attaching a lead it would continue strolling as if there was no lead. A simple reattaching of the lead fixes this. (the lead actually is attached, it's no graphic glitch, since the item drops upon unleashing)