When I examine in my inventory (dragged out of mount window to a bag) the pop up to convert to house item does not show up. I have setting set so no windows are off screen, other mounts convert.
Your saying this like I don't know that. Generally wings and the illusion mounts don't convert and other mounts do. I didn't and can't see why this one wouldn't and thought it was a mistake because it's not the first time this has happened.