main.ctype_ucs failed in buildbot with Data too long for column

main.ctype_ucs                           w2 [ fail ]

        Test ended at 2018-10-31 16:00:28

CURRENT_TEST: main.ctype_ucs

mysqltest: In included file "/usr/share/mysql/mysql-test/include/ctype_numconv.inc": 

included from /usr/share/mysql/mysql-test/t/ctype_ucs.test at line 792:

At line 216: query 'create table t1 as select concat(rand()) as c1' failed: 1406: Data too long for column 'c1' at row 1

The result from queries just before the failure was:

< snip >

hex(concat(round(0.5)))

0031

create table t1 as select concat(round(0.5)) as c1;

show create table t1;

Table	Create Table

t1	CREATE TABLE `t1` (

  `c1` varchar(3) CHARACTER SET ucs2 DEFAULT NULL

) ENGINE=MyISAM DEFAULT CHARSET=latin1

drop table t1;

select hex(concat(sign(0.5)));

hex(concat(sign(0.5)))

0031

create table t1 as select concat(sign(0.5)) as c1;

show create table t1;

Table	Create Table

t1	CREATE TABLE `t1` (

  `c1` varchar(21) CHARACTER SET ucs2 DEFAULT NULL

) ENGINE=MyISAM DEFAULT CHARSET=latin1

drop table t1;

create table t1 as select concat(rand()) as c1;