Animals that go through nether portals disappear (or teleport far away, somehow)

I spent a long time getting wolves for my 9 year old sister, however, as she brought them with her through the nether (the faster way to travel from my house to hers), and went through her portal, she noticed some of her wolves were missing, so she went back to find them in the nether, and then went back and forth between the dimensions multiple times until gradually there wasn't any wolves left, and she realized the portal stole all her dogs. 

Another time, I went to the jungle for another reason than to find parrots, but lucky me I stumbled upon 2 of them, however this time I had came to the jungle by travelling through the nether, and as I expected, after I sent them through the portal, they weren't waiting on the other side of the portal for me. 

(This might be related to another bug I will soon post, about how my sister's cats and parrots that disappeared by closing the LAN world, teleported back to my sister when I loaded in a random chunk on another journey.)