Deleting original swatch of teeth makes duplicate

I'm making an override of the braces. While adding swatches, I deleted the first one, and when I tested the override in CAS, the game seemed to generate an extra swatch that uses the default texture (the teeth texture that is attached to the head). Many of the game's teeth don't have their own textures and use the head's texture instead, but the default braces do have their own texture, so I thought this behavior was odd. 

The same thing happened when I made an override of the buck teeth. I hadn't added any swatches, but I think I changed the color of the swatch thumbnail accidentally.

I can fix the problem by making a new override and making sure not to delete the first swatch (or change the color of the first swatch thumbnail), but since I'm moving around the swatches while I test, it's easy to forget which was the initial one.

Is this a bug with S4S or just part of how the game works?