Add warning and forgotten property sheet.

bt5/erp5_wendelin/DocumentTemplateItem/portal_components/document.erp5.DataStream.py

@@ -47,6 +47,7 @@ class DataStream(BigFile):
   # Declarative properties
   property_sheets = ( PropertySheet.CategoryCore
                     , PropertySheet.SortIndex
+                    , PropertySheet.DataStream
                     )
 
   def readChunkList(self, start_offset, end_offset):

bt5/erp5_wendelin/SkinTemplateItem/portal_skins/erp5_wendelin/DataStream_readChunkListAndTransform.xml

@@ -64,7 +64,8 @@ if transform_script_id is not None:\n
   if transform_script is not None:\n
     start, end = transform_script(data_stream_chunk_list, start, end)\n
 \n
-# store current position offset in Data Stream\n
+# [warning] store current position offset in Data Stream, this can cause easily \n
+# ConflictErrors and it spawns re-index activities on DataStream\n
 data_stream.setOffset(end)\n
 \n
 # start another read in another activity\n