I spent some time this afternoon looking into this problem, and I believe the problem only happens when permanent party members that you have recruited are not included in NVariety. I tested on a Human Noble Female with Wynne and the temporary party members excluded from NVariety, and both mods worked fine before Wynne was recruited, but were glitchy after Wynne was recruited. From before Wynne was recruited, I checked Eleanor (excluded from NVariety) in the origin, Leliana and Morrigan (both included in NVariety - both with and without using the potion on them), and the girls at the Pearl in Denerim, and they were all fine regardless of whether my PC had used the potion or not. With Wynne recruited, I could no longer use the potion to revert my PC to the default model. After using the potion on my PC, Wynne used the same model as my PC. I could use the potion on Leliana and Morrigan to get their NVariety models, but when they were in the default state they also used my PC's model. I reconfigured NVariety to include Wynne, and checked Leliana, Morrigan, Wynne (now all in NVariety), the girls at the Pearl and the human female corpse in Fort Drakon, and all were fine. I also tested on a Human Noble Male PC in both the origin and Ostagar, and checked that the Ostagar prisoner (a live, non-party-member NPC), Dairren (a corpse), Daveth (temporary party member in NVariety), Jory (temporary party member not in NVariety) and Alistair (permanent party member in NVariety) all used the expected models - and it worked perfectly.