We discover that actually maelstro automatically check the box "customizeFeatureType" on the target GeoServer although it is not set on the source GeoServer.
So maelstro does not respect the configuration of the original layer !
We discovered that when the "customized attributes" is activated it freezes the list of the attributes even if there is new attributes added on the table in the database !
We mainly use SQL datasource as "SELECT * FROM my_table" for our layers.