It is now possible to build above the nether bedrock and consequently mobs are appearing, After crossing the bedrock using a ladder and an enderpearl (another bug) the player has access to the top of the nether, After having access to the top of the nether it is possible to place blocks and cause mobs to spawn. This bug is unacceptable, I tested this in the Bedrock version and obviously this bug does not exist there, there is a difference between the height of the nether between the two versions and this difference causes this possibility of bypassing the ceiling of the nether and being able to build anyway after bedrock