KEY partitioning not using all partitions?

[Brian Long]

I've created a table partitioned by key into 4 partitions. When I insert 17M rows, all rows go into only 2 out of 4 of the partitions. The column being partitioned on contains an MD2 hash, e.g. random bits, so I can't fathom how statistically improbable it would be to have the partitioning function send everything to only 2 out of 4 of the partitions. I must be doing something wrong... any ideas?

create table d_my_table (
text_hash char(22),
...
primary key(text_hash)
) partition by key(text_hash) (
partition p1
data directory = '/dist/app/mysql-5.1.30-linux-x86_64-glibc23/data-sdb/'
index directory = '/dist/app/mysql-5.1.30-linux-x86_64-glibc23/data-sdb/' ,
partition p2
data directory = '/dist/app/mysql-5.1.30-linux-x86_64-glibc23/data-sdc/'
index directory = '/dist/app/mysql-5.1.30-linux-x86_64-glibc23/data-sdc/',
partition p3
data directory = '/dist/app/mysql-5.1.30-linux-x86_64-glibc23/data-sdd/'
index directory = '/dist/app/mysql-5.1.30-linux-x86_64-glibc23/data-sdd/',
partition p4
data directory = '/dist/app/mysql-5.1.30-linux-x86_64-glibc23/data-sde/'
index directory = '/dist/app/mysql-5.1.30-linux-x86_64-glibc23/data-sde/'
);