Idle in transaction ????

we've just started using zeos postgresql db components in delphi and i've
noticed that vacuum is hanging in postgres.

if i do ps auxf i get the following

postgres 332 0.0 0.5 13832 1344 ? S 14:24 0:00
/usr/local/pgsql/bin/./postmaster -i -o -F -B 1024 -N 128
postgres 722 0.0 1.3 14704 3496 ? S 14:55 0:00 \_ postgres:
postgres ohm 10.139.13.112 idle in transact
postgres 752 0.1 1.8 14580 4740 ? S 15:04 0:01 \_ postgres:
iain ohm 10.139.13.187 idle
postgres 1086 0.5 1.3 14620 3360 ? S 15:23 0:00 \_ postgres:
postgres ohm [local] VACUUM waiting

it's the 'idle in transact' that i'm puzzled about and i'm assuming it's
idel within a transaction block ...

can anyone help ???

Steve