I have to agree with this. On the workshop I'm very annoyed when I use a specific filter such as "Addon Type: Terrain" and scenarios pop up.
"Addon Type: Terrain" is for custom maps to be published under. Not missions. This is a rampant issue with nigh every category and needs to be fixed. This wouldn't directly address the issue in full, but it would help to mitigate more things being published falsely.