I’ve created a post under the “Troubleshooting and Bugs” category [Reset Photo(s) only Unconverts Photo(s)] outlining this unexpected behaviour. Not sure how often Nate reviews those posts prior to pushing out updates, but figured that could be my small contribution to the improvement of NLP. 
I will keep your suggestions in mind if a complete reset of the raw image is needed. Lightroom’s “Reset” button does return the Profile back to the default Adobe Color, but the NLP settings still persist on re-converting the negative, requiring a “reset” in the EDIT tab - or, as you suggest, creating a duplicate file. Hopefully that will be an uncommon occurrence!