Confirmed on OS X. (15w43c) Also a "less aggressive" workaround from the lava solution... if a block of water can be placed 3-4 blocks directly above the boat-with-horse, the horse will dismount as the boat is forced under water. Both may then be interacted with as expected.
Eclypseon
Confirmed on OS X. (15w43c)
Also a "less aggressive" workaround from the lava solution... if a block of water can be placed 3-4 blocks directly above the boat-with-horse, the horse will dismount as the boat is forced under water. Both may then be interacted with as expected.