This ONLY happens if your model is set to Process Client Side:

As of Spark 12.0.11 using pages in v1, having a field with required at the UI-level and marking “Add None Option” causes the field to always default to that none value, even if there is already a saved value in that field. This happens if you have a custom none label or not. 

As noted above, the fix is to uncheck Process Model Client Side