Incorrect Calculation while using Avg Function

Avg Function reports incorrect query results in SELECT.

show variables like '%optimizer_switch%';

index_merge=on,index_merge_union=on,index_merge_sort_union=on,index_merge_intersection=on,index_merge_sort_intersection=off,engine_condition_pushdown=off,index_condition_pushdown=on,derived_merge=on,derived_with_keys=on,firstmatch=on,loosescan=on,materialization=on,in_to_exists=on,semijoin=on,partial_match_rowid_merge=on,partial_match_table_scan=on,subquery_cache=on,mrr=off,mrr_cost_based=off,mrr_sort_keys=off,outer_join_with_cache=on,semijoin_with_cache=on,join_cache_incremental=on,join_cache_hashed=on,join_cache_bka=on,optimize_join_buffer_size=on,table_elimination=on,extended_keys=on,exists_to_in=on,orderby_uses_equalities=on,condition_pushdown_for_derived=on,split_materialized=on,condition_pushdown_for_subquery=on,rowid_filter=on,condition_pushdown_from_having=on

CREATE TABLE `avg_calc_test` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`name` varchar(255) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=latin1

INSERT INTO avg_calc_test (name) values ('ORANGE'), ('BLUE'), ('BLACK'), ('ORANGE'), ('BLACK');

– correct result 2.00
SELECT
AVG(CASE WHEN name = 'orange' THEN 3 WHEN name = 'blue' THEN 2 WHEN name = 'black' THEN 1 ELSE 0 END) AS metric_val
FROM avg_calc_test;

--Incorrect result 0.99
SELECT * FROM (
SELECT
AVG(CASE WHEN name = 'orange' THEN 3 WHEN name = 'blue' THEN 2 WHEN name = 'black' THEN 1 ELSE 0 END) AS metric_val
FROM avg_calc_test
) T;

SET optimizer_switch="split_materialized=off";
--Incorrect result 0.99
SELECT * FROM (
SELECT
AVG(CASE WHEN name = 'orange' THEN 3 WHEN name = 'blue' THEN 2 WHEN name = 'black' THEN 1 ELSE 0 END) AS metric_val
FROM avg_calc_test
) T;