Argh! Thank you for this report!
I have attempted to fix it now twice, and it works on my end, and for some reason no matter what I am doing, it still bugs out when others play! I will take this and attempt for a third time to get this achievement working for the next coming patch :)
Thank you so much for taking the time xeb to let me know about this! This bug haunts my dreams :P
<3 MoltenCherry