fix issue #111

This alway happens, when an edit form has validation errors and returns
back with the prefilled values from the request which are in fact
basestring types and get joined by the separator as described above.

CHANGES.rst

@@ -4,6 +4,10 @@ Changelog
 1.9.1 (unreleased)
 ------------------
 
+- Fix value for at.AjaxSelectWidget when the edit form returns with
+  validation errors
+  [petschki]
+
 - Use the RAW text for Archetypes based TinyMCE content, this fixes
   image handling with TinyMCE.
   [pcdummy]

plone/app/widgets/at.py

@@ -359,8 +359,10 @@ def _base_args(self, context, field, request):
             self.vocabulary = vocabulary_factory
 
         args['name'] = field.getName()
-        args['value'] = self.separator.join(request.get(
-            field.getName(), field.getAccessor(context)()))
+        value = request.get(field.getName(), field.getAccessor(context)())
+        if isinstance(value, basestring):
+            value = value.split(self.separator)
+        args['value'] = self.separator.join(value)
 
         args.setdefault('pattern_options', {})
         args['pattern_options'] = dict_merge(