Unable to spawn passive mobs.

Unable to spawn passive mobs, making mob farms or waiting in new survival or creative worlds does not spawn any passive mobs.

What I expected to happen was...:
with making a passive mob farm, i was expecting that passive mobs would spawn under correct conditions, but despite multiple try's, nothing has happened.

What actually happened was...:
no passive mobs spawned whatsoever.

Steps to Reproduce:
1. create a passive mob farm under all the correct conditions
2. wait expected time for spawn, which is when nothing happens. 
3. ...