prevent validators from getting inserted twice

flask_admin/contrib/mongoengine/form.py

+from copy import deepcopy
+
 from mongoengine import ReferenceField, ListField
 from mongoengine.base import BaseDocument, DocumentMetaclass, get_document
 
@@ -68,7 +70,8 @@ class CustomModelConverter(orm.ModelConverter):
         }
 
         if field_args:
-            kwargs.update(field_args)
+            # prevent modification of self.form_args
+            kwargs.update(deepcopy(field_args))
 
         if field.required:
             kwargs['validators'].append(validators.InputRequired())

flask_admin/contrib/sqla/form.py

 import warnings
 
+from copy import deepcopy
+
 from wtforms import fields, validators
 from sqlalchemy import Boolean, Column
 
@@ -147,7 +149,8 @@ class AdminModelConverter(ModelConverterBase):
         }
 
         if field_args:
-            kwargs.update(field_args)
+            # prevent modification of self.form_args
+            kwargs.update(deepcopy(field_args))
 
         # Check if it is relation or property
         if hasattr(prop, 'direction'):