So after further investigations I've made some discovery .
First I know that you've made some fix on the beefale herding mechanic on the game update 280490 .
-Fixed bug causing Baby Beefalo to sometimes split from their herd when fully grown.
-Fixed bug preventing herds from merging properly
BUT the thing I didn't know that the goat and the Beefalo shard the same herd.lua file .
I'm not sure anymore this is a bug then .... But Goat where not mentionned is this patchnote at all . Intended mechanic or bug ? Klei will decide the fate of my goat herd now .