Tried renaming my Walls.dmi (Icon File) to Art\Walls to make a new folder for it to be placed in. It didn't work though so I created a new icon file and named it Art\Wall. I then renamed the Walls.dmi to Art\Walls.dmi . It worked this time and was put into the Art folder. I then went to my map file and saw that anything that was in Walls.dmi was shown as if it didn't have an icon.
EDIT: It also seems that when I renamed my Players.dmi(Icon file) to Art\Players my players base wouldn't show up. It seems once you rename the .dmi file it shows up again. Not sure why only certain .dmi files are disappearing and some aren't when I rename them to be in folders.
Code Snippet (if applicable) to Reproduce Problem:
turf // The code seems
Walls
Wall
icon = 'Walls.dmi'
icon_state = "wall"
density = 1
Workarounds:
Tried deleteing the .dmi and making a new one with the same name and it still didn't work.
The only thing that seemed to work was to rename the Walls.dmi file to something entirely new.