Rabbits were trapped by fences

Rabbits were trapped by fences(two blocks high).

What I expected to happen was...:

The rabbits were put at an area circled by fences.
Eventually, when they were scared when I was close to them, they jumped and ran quick randomly, and they were trapped by the fence (two blocks high).

What actually happened was...:

The rabbits cannot move away from the fence afterward.

Steps to Reproduce:
1. Circle an area with fences (two blocks high);
2. Put some rabbits inside the area;
3. Players get close to it without flowers or carrot(not to let them trust you)
4. They were trapped (See attachment - the rabbits at behind)