Wrong "Truncated incorrect DECIMAL value" warning/error in recent releases

ERROR 1292 (22007) at line 15: Truncated incorrect DECIMAL value: '#'

drop table if exists t1;

drop table if exists t2;

create table t1(c1 varchar(1));

create table t2(c1 varchar(1));

set session sql_mode = STRICT_TRANS_TABLES;

insert into t1(c1) values('#');

insert into t2(c1)

  select if(c1 = '#', c1 = 0, c1) as c1

  from t1;