It has always done that with the formal dress, even when i don't want it to. Best bet to get it to work, is to set it to some other costume, like Skants, or Khan's outfit, that no one cares about in the mods options.
I could be a idiot or it's the mod's doing but, every time I install it. it just affects the formal clothing and not the ones I had selected (How can formal even be affected with no option to do so?). I even just selected skant and nothing else except for texture options, and it still affects only formal clothing.