Mob AI don't use Jump Boost

When you apply Jump Boost I or II to a mob other than a spider, cave spider, bat, ghast, slime, magma slime using a Splash Potion of Leaping I or II, the Mob will not jump over fences etc. But if there is a "normal" way to jump up the Jump Boost will have its effect (correct).

What I expect to happen:
The Mob realizes to be able to jump higher and finds other ways to the target.

What happens:
The Mob jumps higher but uses only ways possible without jump boost.

Steps to reproduce:

1. Place down a 2 Blocks high wall using a solid material (e.g. Sandstone)
2. Spawn a Sheep
3. Apply Jump Boost II to the Sheep using a Splash Potion of Leaping II
4. Use a Leash to try to get the Sheep above the wall (should be possible)
5. Realize that it's impossible