Player Takes Damage Going Through Nether Portal

^{Update by [Mojang] Mega_Spud (Jay Wells):}
Steps to Reproduce:

1. Create a new world (No experiments, any seed, tested with several)
2. Build and light a nether portal in the overworld
3. Travel through
4. In the nether, move the nether portal down by 1 block
   • (break the top and bottom of the portal frame and place new blocks to move down by y1, and re-light)
5. Place lava underneath the bottom obsidian blocks
6. Switch to Survival
7. Travel through the portal to the Overworld
   • There's a ~50% chance that you will take half a heart of suffocation damage at this point
8. Now travel back through the portal to the Nether

Observed Results:
The player is loaded into the lava beneath the portal.
As you load into the Nether, you can hear the player taking fire damage, and when you load in visually, you are on fire for several seconds, reducing your health significantly.

Expected Results:
You should not take any unexpected damage when travelling through the portal - the player should be spawned in a safe spot on the base of obsidian portal frame

Screenshots/Videos attached: Yes

Notes:

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Original Description:

When going through nether portals I get a half to a whole heart worth of damage on a regular basis. Also, when going through a nether portal that is suspended above ground I will glitch through the floor and take fall damage from it. In instances where I am above lava I will also catch on fire.

Keywords for search: player suffocation suffocate damage dmg clip inside block spawn safe point nether portal travel travelling traveling overworld nether obsidian frame