"connect" storage engine using table type VEC: cannot use "unsigned" types

I cannot insert into a VEC table any values as soon as I declare a column "unsigned".
Example:

Step 1)

CREATE TABLE test (

  mycol tinyint unsigned

)

DEFAULT CHARSET=utf8 COLLATE=utf8_bin

engine=CONNECT table_type=VEC file_name='test_.vec'

;

Step 2)

insert into test values(1)

;

Result)

ERROR 1296 (HY000): Got error 122 'Non matching Value types' from CONNECT

Tried with different integer types ("integer", "bigint"), but the result is always the same.
Am I doing something wrong?
Docs (https://mariadb.com/kb/en/library/connect-data-types/#unsigned-numeric-types) state that unsigned should not be a problem (from what I understood mariadb 10.1.31 & .34 should be using a connect-engine more recent than 1.01.0010)
Thx

p.s.: explicitly used collate & charset as I have in "my.cnf":

character-set-server = utf8

collation-server = utf8_bin