Quote from Animefr3ak
I'm not sure if anybody is getting the same bug on multi as me but every time i tame a dog and just leave him at my base and then come back he'll be gone?
Tame and herded creatures despawn if they can move more than 20 blocks in any direction. Build a "dog house" and you'll be set. Note that animals don't really like to go through doors (or any 1 wide) space, and they can "glitch" into the walls and even die doing so. I think that is related to the bug where mobs can be seen "teleporting" into and out of their enclosures.