If I use a name tag on a mob, it works and goes onto them but as soon as I get off the server and come back its gone.

So you use the anvil, make a name tag with lets say the name bob, you use it on a mob, it looks fine, then you exit the server and join back in, the name tag is not there anymore and its gone, the little bar that shows up above the mob's head is gone and you don't get your name tag back.

(Confused about this a little but I use minecraft on a Samsung Galaxy Tablet tab a)