Virtual column set to NULL using load data infile

create table t1 ( c1 varchar(10), c2 varchar(10), c3 int ); 

insert into t1 values ("a" , "b", 1),   ("a" , "b", 2);

create table t2 like t1 ; 

alter table t2 add column c4 bigint unsigned as (CONV(LEFT(MD5(concat(c1,c2,c3)), 16), 16, 10)) persistent unique key; 

select * into outfile 't1.csv' from t1;

load data infile 't1.csv' into table t2 ;

select * from t2;

select "Wrong c4";

insert into t2 (c1,c2,c3) values ("a" , "b", 4);

select * from t2;

select "correct c4";

a	b	1	NULL

a	b	2	NULL

a	b	4	15541743660496249717