The UKC has adopted a new breed standard for the Mountain Feist, which requires ears to be upright. The standard went into effect on January 1, 2020. Here is the language from the UKC website:
Ears are v-shaped, set at the outside edges of the skull. Ears must be erect. Note: Ear carriage may not stabilize until a dog is mature; therefore, dogs under one year of age should not be penalized for variations in ear carriage.
Disqualification: Cropped ears. Ears not erect.