Expected behavior:

Put EntityTag on Zombie spawn egg:

/give @p spawn_egg 1 0 {EntityTag:{id:"minecraft:zombie",IsBaby:0b,HandItems:[],ArmorItems:[]}}

For 1.13:

/give @p minecraft:zombie_spawn_egg{EntityTag:{IsBaby:0b,HandItems:[],ArmorItems:[]}}

Spawn large number of zombies and they should all be identical.

Actual behavior:

Zombies have varied equipment and type as they would without EntityTag.

This is an issue for the client only; the server has the correct data. Logging out and back in will fix client-side issues.