default engine never transfers vbuckets

When I try to do a rebalance with a memcached bucket type, vbucketmigrator exits with:

542,70 sean@Sean-Lynchs-MacBook-Pro:~/northscale/ns_server$ ./bin/vbucketmigrator/vbucketmigrator -a memcached -h 127.0.0.1:12000 -d 127.0.0.1:12004 -vvv -t -b 3
Enter password:
Connecting to downstream

{Sock 127.0.0.1:12004}

for 3
Authenticating towards:

{Sock 127.0.0.1:12004}

Authenticated towards:

{Sock 127.0.0.1:12004}

Connecting to source: 127.0.0.1:12000
Authenticating towards:

{Sock 127.0.0.1:12000}

Authenticated towards:

{Sock 127.0.0.1:12000}

Did not move enough vbuckets in takeover: 0/1

memcached says:

Tap client connect closed (46). Putting it (0x10062a328) in pending close
OK, time to nuke: 0x10061b3e8 (3992 < 3994)

I suspect these two things are related.

This is blocking testing rebalance with the memcached bucket type.