Baby cows used to die in 13w snapshots and sometimes in 1.5 pre

In my survival world, I was breeding my cows. Everything went all right, the baby cow appeared, but later when I came back, there were still two cows and some beef on the floor. The pen was in a cliff, so I tried expanding it, (maybe it suffocated)but when I came back, there were still two cows.
When I updated to 1.5 Pre release, It worked fine, but I think some baby cows died too. So I'm not sure if its fixed or not.