The subsystem=datasource/data-source=* resource has a connection-properties attribute and a connection-properties sub-resource. Since DMR is a tree structure each child must have a unique key. Since the parent resource has a connection-properties attribute and sub-resource with a read-resource operation you will only get one of the values.

Also writing to the connection-properties attribute fails to marshal the XML since marshaller expects the value to look something like

{ "key" => { "value" => "real-value" } }

But the resource definition expects

{ "key" => "real-value" }

The attribute does not appear to be in EAP 6.4. It is however in WildFly 8.x and 9.x. Some further research should be done, but the attribute could likely be removed. Not having the attribute would also be more consistent with XA data sources.