Cows gathering into corner

Please could you look into what appears to be a glitch I've noticed for some time. I have 15+ cows surrounded by spruce fence and three gates spaced around. Every now and then, I look and every one of the cows are forcing their way into one corner of the compound for seemingly no reason. They remain like that even if I enter and walk right through them. The only way I know how to break this behaviour, until it happens again relatively soon after, is by holding wheat. They naturally then all start to follow me and when I hold a different item, the cows then go about random-direction walking as I'd want them to. Before long, however, the cows are bunching again... into the same corner. I currently also have just one sheep in there with them. Not sure if this causes the issue for some obscure reason but will remove the sheep to see. One block higher from the cow compound and about 5 blocks distant is a chicken compound. Can't see why the cows would be trying to get to the chickens but I thought I'd give you this info too. If this bunching behaviour is 'normal' and/or intentional, I'd like to know why. Good luck!