I've read here and there that repeated battling of the spirits was hotfixed recently, but I couldn't find any mention of it in the patch notes. I couldn't tell therefore, whether the ability to battle these guys was broken from the start of MoP and is now fixed, or if it was working as intended before and is now broken, so I submitted a ticket. Here's the GM response:
Heya Xxxxxx, Game Master Senkayn here!
To be honest I've not heard of this before. It may simply have become broken with 5.4.7 as I'm not seeing any information on it one way or the other. Since I’m not able to find any current reports or work-arounds regarding this issue, I’ve taken the information you’ve provided to me and submitted a report to our QA and Development teams.
The information you’ve provided will be helpful to both the QA and Development teams and they’ll begin investigating, attempting to re-create, and then fixing this particular issue.
If, like me, you'd like to get back to power leveling your hundreds of pets (a great idea while we're in this end-of-the-expansion lull I say), please open a ticket on this so it gets a little more attention.