When a llama, horse, mule, etc. is spawned on a large glass platform, the player can still ride the animal, but cannot tame it. There are no love hearts, nor will the player be ejected from the animal. In my test with trader/llamas, feeding hay bales did not change anything either.

To reproduce:

1. Create a large superflat world with a single layer of glass.
2. Spawn an animal (Ex: Trader Llama) and try to tame it. The animal will show no response.
3. Replace some of the glass layer with solid blocks such as concrete.
4. Spawning an animal on the solid block platform and mounting it will result in the usual outcomes of either taming it or being ejected.

I've attached a world download that can be used for testing this. The bug is apparent with animals on the red/clear glass, but the behavior is normal on the lime concrete area.