Gluster users - May 2012 - replace-brick does not complete for replicated volume

I have a replicated volume comprising 2 bricks on 2 different storage servers. I
tried to migrate a brick on server-a to another directory with "gluster
volume replace-brick replicated server-a:/glusterfs/replicated-old
server-a:/glusterfs/replicated-new start" but running "gluster volume
replace-brick replicated server-a:/glusterfs/replicated-old
server-a:/glusterfs/replicated-new status" after about 5mins returned
"status unknown".

There were no further changes to the size of the new brick after this and the
new brick was not the same size as the old brick. I had no such problems with a
single brick distributed volume. I tried looking in the glusterfs logs for clues
but it's not apparent to me what I should be looking for.