[Plugin: Custom Permalinks] One Category not accepting any permalink

I am using the Custom permalinks plugin. It has worked great for me to date. However, I have one recently added category that will not accept any value I put into the custom permalink field.

The name of the category is Rice Paper – Color Study with a slug of ricepaper-colorstudy.

The default permalink for the category is
https://theviolent.net/art/photoshop/ricepaper-colorstudy/

The custom pemalink I would like is
https://theviolent.net/ricepaper-colorstudy/

As I said though, no value is accepted. Anyone have any ideas why this single category is not working with the plugin?

Thanks!!
–giant slayer