Tamed animals disappear to Nether

After taming a pack of wolves, I went to my home near a nether portal and went to bed. When the night passed the wolves were gone with no sign of them.Went to tame another pack of wolves and the same exact thing happened plus my cat disappeared too. Went into the Nether and all of the wolves were there (many on fire) also the cat was there too. It burned to death. _