I expected Sheep to wander around aimlessly in my creative world.

Instead, they will all move into a certain area/direction of the map. I have tried things to stop this like...
*Changing the Grass to Stone
*Putting up Fences
*Building Structures to obstruct the area
But they still gather in the area, constantly.
I have provided a screenshot of the area they gather in. I constantly pull them away with leads only to find them all there again a few minutes later.

I do not know what causes this to happen, so I cannot provide steps to how it is done.