Array Index WHEN clause and query named parameters not working

create index ix1 on default(DISTINCT ARRAY v.lname FOR v IN names WHEN v.mname = "abc" END);

EXPLAIN SELECT 1 FROM default WHERE ANY v IN names SATISFIES v.lname = "xyz" AND  v.mname = "abc" END;  -- works

cbq> \set -$mname  "abc";

cbq> EXPLAIN SELECT 1 FROM default WHERE ANY v IN names SATISFIES v.lname = "xyz" AND  v.mname = $mname END;

{

    "requestID": "adc9c3a6-4904-492c-a15b-94c6b3cca802",

    "errors": [

        {

            "code": 4000,

            "msg": "No index available on keyspace default that matches your query. Use CREATE INDEX or CREATE PRIMARY INDEX to create an index, or check that your expected index is online."

        }

    ],

    "status": "fatal",

    "metrics": {

        "elapsedTime": "2.189019ms",

        "executionTime": "2.021909ms",

        "resultCount": 0,

        "resultSize": 0,

        "errorCount": 1

    }

}