Mixed domain with EAP 6 slaves: data sources operations broken

[domain@127.0.0.100:9990 /] /host=eap640/server=server-one/subsystem=datasources/data-source=ExampleDS:test-connection-in-pool
{
    "outcome" => "failed",
    "failure-description" => "WFLYCTL0297: Transforming operation {
    \"address\" => [
        (\"host\" => \"eap640\"),
        (\"server\" => \"server-one\"),
        (\"subsystem\" => \"datasources\"),
        (\"data-source\" => \"ExampleDS\")
    ],
    \"operation\" => \"test-connection-in-pool\",
    \"operation-headers\" => {
        \"caller-type\" => \"user\",
        \"access-mechanism\" => \"NATIVE\",
        \"domain-uuid\" => \"ae186a65-8c76-41d0-bd23-79154b5f92f7\"
    }
} at resource [
    (\"host\" => \"eap640\"),
    (\"server\" => \"server-one\"),
    (\"subsystem\" => \"datasources\"),
    (\"data-source\" => \"ExampleDS\")
] to subsystem 'datasources' model version '1.3.0' -- attributes [connection-url] WFLYCTL0336: The following attributes are nillable in the current model but must be defined in the target model version: [connection-url]",
    "rolled-back" => true,
    "result" => [true]
}