I will tame a couple dogs (and sometimes breed them) and after varying amounts of time, the dogs will despawn in spite of the fact that they have been tamed by me. this has occurred both while they are sitting at my base/outside, and while they are running around following me. The first couple times this occurred, it was with spawned in dogs. Other people who did not cheat for dogs on the server were unaffected. But the most recent time I tamed dogs I found in the wild and both my dogs and the dogs belonging to the other people on the server despawned.
This has also occurred while LANing, but I assumed it was because I was taming dogs on someone else's single player world while it was open to LAN.