N1QL: Covered query with meta().type in where clause not giving correct results

Index created:
CREATE INDEX `idxcover` ON `default`((meta(`default`).`type`),`name`)

select query:
explain SELECT count(meta(default).type) FROM default where meta(default).type = "json" ;'
this uses the right index:

[
{
"plan": {
"#operator": "Sequence",
"~children": [
{
"#operator": "IndexScan",
"covers": [
"cover ((meta(`default`).`type`))",
"cover ((`default`.`name`))",
"cover ((meta(`default`).`id`))"
],
"index": "idxcover",
"keyspace": "default",
"namespace": "default",
"spans": [
{
"Range":

{ "High": [ "successor(\"json\")" ], "Inclusion": 1, "Low": [ "\"json\"" ] }

}
],
"using": "gsi"
},
{
"#operator": "Parallel",
"~child": {
"#operator": "Sequence",
"~children": [

{ "#operator": "Filter", "condition": "(cover ((meta(`default`).`type`)) = \"json\")" }

,

{ "#operator": "InitialGroup", "aggregates": [ "count(cover ((meta(`default`).`type`)))" ], "group_keys": [] }

]
}
},

{ "#operator": "IntermediateGroup", "aggregates": [ "count(cover ((meta(`default`).`type`)))" ], "group_keys": [] }

,

{ "#operator": "FinalGroup", "aggregates": [ "count(cover ((meta(`default`).`type`)))" ], "group_keys": [] }

,
{
"#operator": "Parallel",
"~child": {
"#operator": "Sequence",
"~children": [
{
"#operator": "InitialProject",
"result_terms": [

{ "expr": "count(cover ((meta(`default`).`type`)))" }

]
},

{ "#operator": "FinalProject" }

]
}
}
]
},
"text": "SELECT count(meta(default).type) FROM default where meta(default).type = \"json\""
}
]

Result of
SELECT count(meta(default).type) FROM default where meta(default).type = "json" ;

[

{ "$1": 0 }

]

Though same query gives correct result with primary index:
SELECT meta(default).type FROM default use index(`#primary`) where meta(default).type = "json" ;

gives 1680 documents.