Steps to reproduce:
1. Mount Horse
2. Log off and Reconnect
3. Dismount horse
4. Punch horse (MC-16156)
The game now thinks you are holding shift, so if you try to get back on the horse, it will only show the inventory. (To fix, press the shift button once, that will unlock it.)
Linked issues
is duplicated by 4
MC-16300
Saddle/Armor interface is buggy
Resolved
MC-16651
Sometimes you cant ride on horses.
Resolved
MC-16723
When A Horse Is Clicked With Chest, You Cannot Get On It And It Keeps On Opening Up The Horses Inventory (2 Bugs If you read it)
Resolved
MC-16724
Changing gamemode and ride a horse
Resolved
Confirmed.
No need to punch the horse, some other things (don't know which) trigger this issue too.