Horses fail to tame or throw off. /Summoned tame horses do not move under player

Conditions:
All Trials: Single Player Survival & Creative
All Trials: Donkey & Horse
Trial 1. Player riding an untamed horse
Trial 2. Riding a tamed horse with saddle
(Note: Tamed horse was only available by /summon in Trial 2)

Expected Outcomes:
1. Horse will buck player off and/or will tame
2. Horse will respond to directional keys in the same manner as a player walking.

Actual Outcomes:
1. Horse does not tame after +5 minutes. Horse bucks but player is not dislodged. Horse may move slightly more erratically than when unridden. Horse bucks =/< than frequency of an unridden horse.
2. Horse is unresponsive and remains immobile.
All Outcomes: Horse & Donkey inventory GUI behaves as expected.

Additional information:
Identical trials repeated twice with same outcomes.