Zombies moving towards villagers or iron golems from a long distance move very slowly

Video: https://youtu.be/Yhps-VCt_r0

If you summon a zombie with increased follow range, they will come toward you from a further distance.

What I expected to happen was...
If a zombie, with increased follow range (e.g. 160 blocks), sees a villager or iron golem from about that distance, it should walk towards its target with its arms up, and eventually reach it.

What actually happened was...
The zombie looked towards the villager. It put its arms up. But it moved very, very slowly.
If, after a very long time it walks closer, or if you spawn a second zombie closer to the villager, it will get back to its normal speed. If you spawn a second villager near the zombie, it will probably change targets to the new villager and pursue it at its normal speed.

Steps to Reproduce:
1. Summon a zombie with increased follow range using the following command:

/summon Zombie ~ ~ ~ {Attributes:[{Name:generic.followRange,Base:160}],PersistenceRequired:1}

2. Spawn a villager about that distance away. There should be a clear view of sight for best results.

3. The zombie will move really slowly towards it with its arms up.

Other notes:
Zombies with increased follow range will still see you from that very long distance, but they will still move towards a player in survival or adventure mode at the same speed as normal. This problem is isolated to villagers and iron golems alone.