How to reproduce
1. Use a horse spawn egg to spawn a horse
2. Right-click on it with a normal item (horse rejects it)
3. Right-click on it with a creeper spawn egg (horse is mounted)
Applies to any spawn egg, except for the horse spawn egg itself (that will spawn a baby as expected).
Affects horses, donkeys, llamas, etc. Does not affect saddled pigs.
Linked issues
relates to
Comments
My apologies for the resolve/reopen, after noticing MC-127386 was fixed I tested again and used the same spawn egg, which now does not cause the behavior. Any other spawn egg does.
Can't reproduce this issue in 18w22c

@unknown, this can still be reproduced in 1.13-pre1
Affects 18w09a