northern side of mud brick stairs flipped

This is not an issue with the mud brick stairs

The mud block parents a unique block model called cube_north_west_mirrored_all which mirrors the north and west faces.

From the Json file:

{
  "parent": "minecraft:block/cube_north_west_mirrored_all",
  "textures": {
    "all": "minecraft:block/mud_bricks"
  }
}

As mentioned below, this is an issue with the mud brick blocks, not the mud brick stairs.

Thank you for your report!
We're tracking this issue in MC-250692, so this ticket is being resolved and linked as a duplicate.

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