Only adds standard variant on create

app/models/spree/product_decorator.rb

@@ -21,7 +21,7 @@ Spree::Product.class_eval do
   attr_accessible :supplier_id, :primary_taxon_id, :distributor_ids, :product_distributions_attributes, :group_buy, :group_buy_unit_size
   attr_accessible :variant_unit, :variant_unit_scale, :variant_unit_name, :unit_value, :unit_description, :notes, :images_attributes, :display_as
 
-  before_validation :ensure_standard_variant
+  before_validation :ensure_standard_variant, if: :new_record?
 
   validates_presence_of :supplier
   validates :primary_taxon, presence: { message: "^Product Category can't be blank" }

spec/models/spree/product_spec.rb

@@ -106,6 +106,11 @@ module Spree
             standard_variant = product.variants(:reload).first
             expect(standard_variant.price).to eq product.master.price
           end
+
+          it "only duplicates master variant on initial save" do
+            product.save!
+            expect(product.variants(:reload).length).to eq 1
+          end
         end
 
         context "when the unit is items" do