Resource packs aren't unloaded after disabling them in the menu

When a texture pack is selected, than it is turned off (with the arrow facing left), than you click done and go into a game. If you try and delete the resource pack that was selected but not anymore from the resource pack folder, it says the program is still using it. However, if you play a world, than leave, you can delete them right from the file. Why is that? That's not right. Plz fix!