Hit-boxes with mobs/fences

When I was playing in survival mode in this new snapshot, I gathered a few passive/farmable mobs (examples: cows, rabbits, sheep, etc...) like most players usually do... But I noticed something strange when I went to breed the rabbits I have corralled. When bread with the carrots I noticed that one of the rabbits were stuck in the fence. (sounds crazy but listen to this) The rabbit's hit-box (for clarification; the area that a player can hit/interact with an entity) was inside the fence's hit-box. But in a way that I could feed it, but not HIT it... I could mine out the fence fine, but the rabbits/chickens kept getting suck SUPER easily... (Larger animals were getting stuck as well, but not as often as these smaller mobs)
Also, when I traveled into the nether for the 1st time on this world, (after I found what I was looking for) I returned to the over-world where I had found a good number of my corralled mobs had ESCAPED! D: I was so confused because they were in a cage... They shouldn't be able to escape... So, I repeated the process, and sure enough it did it again! It's getting difficult to hold these mobs in one place (I haven't the resources to use leads as I can't find any slimes XD)... So that's what I've noticed about the fences/mobs THANKS! 😃
(picture is of the mobs being stuck in the fence...)