vbucketmigrator exit with status 70 and 78

Created an attachment (id=772)
diag of node A

Install ms 1.6.0beta4-74 on 2 ubuntu 9.04 64bit servers.
At node A, create 2 memcached buckets and 2 membase buckets.
Load data to buckets.
At node A, run load against default buckets (1.5 GB).
While the load is running, at node A, add node B to node A.
Rebalance. OK as expected.
After rebalance ended, at node A, click remove server to remove node B (load still running).
Rebalance. work as expected.
Check log page, see vbucketmigrator exited with status 70 and 78
http://screencast.com/t/ajUbT8kfJ