As the changelog of 26.60.28 mentioned:
When dismounting a Strider the passenger will be dismounted onto a block in the location where the passenger is looking on a block that is not Lava and one block away (MCPE-175573)
However, this does not have effects for horses dismounting.
Steps to reproduce the issue
1. Create a new world with creative mode and cheats enabled.
2. Enter the nether (recommended) and find a huge lava area. You can also create a large lava area by yourself.
3. Summon a horse, and give it splash fire resistance potion. Tame it and saddle it.
4. Mount the horse and move it toward the lava, and then try to move towards the land nearby. Ensure that the horse is a block near to the land, and point your crosshair onto the land.
*5. (Optional) You can make a comparative experiment, in which you do the same thing to a strider. And you can observe that, in most cases you will safely dismount without going to lava.Expected result
The player safely dismount, without going down to lava.Actual result
The player will dismount directly into the lava, unlike the case of strider. But I hope that the new dismounting mechanism applies to all mountable mobs (like donkey, mute, llama, minecart, etc).
Thank you for helping us improve Minecraft! We saved your files: