When dismounting from a minecart, the player or mob riding the minecart should be deposited on an adjacent block if one is available.
When dismounting from a minecart, the player or mob is deposited directly above the minecart, even when other valid spaces are available. This can cause suffocation damage to the player or mob if there is a solid block two blocks above the minecart.
- Place any rail, then a minecart on the rail.
- Get in the minecart, then get out of the minecart. (When not on a rail with shift dismounting.)
- Place a solid block above the block where the minecart is sitting with two air block in between to see the suffocation damage.
Based on 1.11.2 decompiled using MCP 9.35 rc1
It looks like the method net.minecraft.entity.EntityLivingBase.dismountEntity(Entity) now shifts down the bounding box it uses for testing block collisions by the ridden entity height.