TokuDB: Auto-increment on a secondary column is accepted, but causes gaps

CREATE TABLE t1 (a char(8), b int AUTO_INCREMENT, PRIMARY KEY (a,b)) ENGINE=TokuDB;

INSERT INTO t1 (a) VALUES ('a'),('b'),('c'),('d'),('e'),('f'),('g'),('h'),('i'),('j');

SELECT LAST_INSERT_ID();

LAST_INSERT_ID()

1

SELECT a,b FROM t1;

a	b

a	1

b	11

c	21

d	31

e	41

f	51

g	61

h	71

i	81

j	91

install soname 'ha_tokudb.so';

CREATE TABLE t1 (a char(8), b int AUTO_INCREMENT, PRIMARY KEY (a,b)) ENGINE=TokuDB;

INSERT INTO t1 (a) VALUES ('a'),('b'),('c'),('d'),('e'),('f'),('g'),('h'),('i'),('j');

SELECT LAST_INSERT_ID();

SELECT a,b FROM t1;

bzr version-info

revision-id: holyfoot@askmonty.org-20130514121908-d6tp4zsdkim0q4dg

revno: 3768

branch-nick: 5.5-hf-tokudb