I believe this is the post Tandy was referring to but couldn't link for those that want to read further:
http://us.battle.net/wow/en/forum/topic/20747864624#1
Jal
Enchanted Broom Update
This issue has now been fixed.
Re: my post of earlier this week on Enchanted Broom. I received a response from a GM.
Originally the broom showed it's actual level in my journal, but when targeted, it showed as level 0, and would not accept a Magic Battle-Stone to upgrade it a level. Today, it shows its actual level when targeted. I just battled with it and it did gain a level. XP gain appeared to be normal. It still will not accept a battle-stone for upgrade.
The response from the GM was:
Greetings Tormentia,
This is Game Master Valestianz, I've just red through your ticket
I checked into this, and had the same issue, so I've forwarded the information to our developers so they can investigate this matter. For the time being, it doesn't seem that there's a workaround for this particular issue, but hopefully it won't take too long to find a solution.
This is fairly troubling if they don't find a solution, because the Enchanted Broom is one of the pets that's critical to getting the Family Familiar achievement in Legion. I would suggest anyone who has this pet and wants the achievement (!!) add to the bug report we have going here: Ok .. can't post link because although a member of PP for years, apparently I don't post here enough.
Just go to Bug Report Forum and search enchanted broom. You should find the post.
Re: my post of earlier this week on Enchanted Broom. I received a response from a GM.
Originally the broom showed it's actual level in my journal, but when targeted, it showed as level 0, and would not accept a Magic Battle-Stone to upgrade it a level. Today, it shows its actual level when targeted. I just battled with it and it did gain a level. XP gain appeared to be normal. It still will not accept a battle-stone for upgrade.
The response from the GM was:
Greetings Tormentia,
This is Game Master Valestianz, I've just red through your ticket
I checked into this, and had the same issue, so I've forwarded the information to our developers so they can investigate this matter. For the time being, it doesn't seem that there's a workaround for this particular issue, but hopefully it won't take too long to find a solution.
This is fairly troubling if they don't find a solution, because the Enchanted Broom is one of the pets that's critical to getting the Family Familiar achievement in Legion. I would suggest anyone who has this pet and wants the achievement (!!) add to the bug report we have going here: Ok .. can't post link because although a member of PP for years, apparently I don't post here enough.
Just go to Bug Report Forum and search enchanted broom. You should find the post.Last edited by Tandy on July 23rd, 2016, 9:13 pm, edited 1 time in total.
Re: Enchanted Broom Update
Jal - Yes, that's the post. TY! 
Re: Enchanted Broom Update
This bug has now been fixed. It's in the list of the latest hot fixes and I just used a stone successfully.