Cursor protocol returns incorrect metadata for group_concat()

create table t1 (f1 int unsigned, f2 varchar(255));

insert into t1 values (1,repeat('a',255)),(2,repeat('b',255));

--enable_metadata

select f2,group_concat(f1) from t1 group by f2;

--disable_metadata

drop table t1;

Catalog	Database	Table	Table_alias	Column	Column_alias	Type	Length	Max length	Is_null	Flags	Decimals	Charsetnr

def	test	t1	t1	f2	f2	253	255	255	Y	0	0	8

def					group_concat(f1)	252	1048576	1	Y	0	0	8

Catalog	Database	Table	Table_alias	Column	Column_alias	Type	Length	Max length	Is_null	Flags	Decimals	Charsetnr

def	test	t1	t1	f2	f2	253	255	255	Y	0	0	8

def					group_concat(f1)	252	16777215	1	Y	16	0	8