app/models/seminar_signup.rb

@@ -69,6 +69,7 @@ class SeminarSignup
           sr.save
         end
       end
+      seminar_main.seminar_signups.delete(self) #avoid resave 
       if seminar_main.unassigned_seminar_signup_ids.delete(id)
         seminar_main.save
       end