This could be true, please everyone do not rush to "test" this fact. We have people looking into it as time allows and they are active. More information will be posted as we know.
did you try the command /pet summon to see if your pet appears?
If you think you're causing this issue, please do it again now! I added a little bit of code to help work out what's wrong.
its the server and himself by the mean time xD dont know if he gave the item to a GM like i advised him to do so, might be interesting to test with someone else.