Fetch the last position for the placeholder to add a correct position…

… to the new created plugin.

cms/api.py

@@ -11,6 +11,7 @@
 from django.conf import settings
 from django.contrib.auth.models import User
 from django.contrib.sites.models import Site
+from django.db.models import Max
 from django.template.defaultfilters import slugify
 from menus.menu_pool import menu_pool
 
@@ -266,10 +267,14 @@ def add_plugin(placeholder, plugin_type, language, position='last-child',
     # validate and normalize plugin type
     plugin_model, plugin_type = _verify_plugin_type(plugin_type)
 
+
+    max_pos = CMSPlugin.objects.filter(language=language,
+        placeholder=placeholder).aggregate(Max('position')).values()[0] or 0
+
     plugin_base = CMSPlugin(
         plugin_type=plugin_type,
         placeholder=placeholder, 
-        position=1, 
+        position=max_pos + 1,
         language=language
     )
     plugin_base.insert_at(target, position=position, save=False)