Sheep leave their pens when I leave the chunk they are in

So I'm encountering this weird bug where whenever I leave the chunk that my sheep pen is is, 1 or 2 of the sheep just seem to escape. I used fences and made sure none of them could escape, so this is clearly a bug. One thing to note though, it seems to be the same sheep which always escape. I have a green sheep which is escaping all the time.