Need help, autotiles won't save icon or masking

KeTTLe

Hey, I'm trying to set up an autotile, but whenever I try to select an icon it won't apply. I can save the tileset, but it deletes all of the masking I've done to it. I can't seem to find a solution to this anywhere. Maybe I'm just dumb :/

Any fixes would be appreciated

exuin

Have you tried opening and closing the editor? :'(