Juggernaut and Mirage Master


So I summoned a juggernaut when I have a bundle of creep.
Then my opponent summoned Mirage Master to copy my juggernaut.
Abyssal Juggernaut description: This minion has +1/+1 for each friendly shadow creep.
My opponent clearly has no creep so I expected a 3/3 instead of a 9/9. Juggernaut normally adjusts stats when creep changes.
When I gained one more creep my juggernaut became a 10/10 while my opponent’s juggernaut stayed 9/9.

So bug or weird interaction? :confused: