Essence-Infused Moonstone

So I got in the mail Essence-Infused Moonstone while my Moonstone, that I had in my keyring, got removed.

I completed all the quests for druid and I used the moonstone to summon Anzu for the mount.

And now I cant put the moonstone that I got in the mail back into keyring.

Is it a bug or something else?

Yes it won't fit in the keyring anymore. It's a known bug. In retail WOTLK its treated as a key in the key ring.