Update ngsi_arcgis_featuretable_sink.md

doc/cygnus-ngsi/flume_extensions_catalogue/ngsi_arcgis_featuretable_sink.md

@@ -42,7 +42,7 @@ Each entity type needs an url and an unique field to be persisted into the featu
 
 NGSIArcgisFeatureTableSink composes each table's url with entitie's `service` and `service path`, to provide multiple tables access. 
 
-Unique field is provided to allow `NGSIArcgisFeatureTableSink` to update existant entities. NGSI `entity type` will be used as unique field name.
+Unique field is provided to allow `NGSIArcgisFeatureTableSink` to update existant entities. NGSI `entity type` will be used as unique field name. This means that a feature named `type` in the Feature Table cannot be filled in by the sink. If Feature Table needs to persist the value of entity type it has to be in a feature different than `type`.
 
 All this parameters, can be customized using Cygnus mapping capabilities.
 
@@ -160,6 +160,11 @@ Connections to `cygnus-ngsi.sinks.arcgis-sink.arcgis_service_url` and `cygnus-ng
 
 [Top](#top)
 
+#### <a name="section2.2.1"></a>About case-sensitivity
+
+**[FIXME #2320](https://github.com/telefonicaid/fiware-cygnus/issues/2320)**. Currently Arcgis sink is case sensitive with the attributes to persist in the Feature Table although arcgis is not case sensitive. This behaviour requires the use of name-mappings to match the case letters of the attribute definition in the Feature Table.
+
+[Top](#top)
 
 ## <a name="section3"></a>Programmers guide
 ### <a name="section3.1"></a>`NGSIArcgisFeatureTableSink` class