You can't sneak-click to access the inventories on horses with an entity riding them

The bug

You can't sneak-click to access the inventories on horses with an entity riding them. However you can access the inventory as usual once the riding entity has been killed / removed from the horse.

Example command:

/summon minecraft:horse ~ ~1 ~ {Type:1,ChestedHorse:1,Tame:1,NoAI:1,Passengers:[{id:"minecraft:armor_stand"}]}