Though I know little of this bug, as players on my server are accidently causing it, I can tell you that there's a horse glitching when breeding. This causes the server to stop responding untill it runs out of memory.

Here's a link to a forum-thread I made earlier:
http://www.spigotmc.org/threads/chunk-render-bug.47069/

This bug has occured for me twice so far. I'm currently still working on fixing the second bug which is hard as I cannot locate the chunk on which the glitched horse is placed.