Rebalance fails (noproc, ns_single_vbucket_mover:mover/6)

The testrunner spatial test
spatialrebalancetests.SpatialRebalanceTests.test_insert_x_docs_during_rebalance,num-docs=10000

fails sometimes. When it fails, it does a rebalance and then returns an error (see below). I've attached the debug log from node 0 (there are 4 nodes) from the time when i happened. The crash report mentions ns_single_vbucket_mover:mover/6.

[2012-05-11 03:42:58,288] - [spatial_helper:120] INFO - inserted 10000 json documents
[2012-05-11 03:42:58,294] - [rest_client:770] INFO - rebalance percentage : 7.8125 %
[2012-05-11 03:43:00,299] - [rest_client:770] INFO - rebalance percentage : 12.5 %
[2012-05-11 03:43:02,305] - [rest_client:770] INFO - rebalance percentage : 18.75 %
[2012-05-11 03:43:04,313] - [rest_client:770] INFO - rebalance percentage : 23.4375 %
[2012-05-11 03:43:06,318] - [rest_client:770] INFO - rebalance percentage : 25.78125 %
[2012-05-11 03:43:08,339] - [rest_client:770] INFO - rebalance percentage : 28.90625 %
[2012-05-11 03:43:10,346] - [rest_client:770] INFO - rebalance percentage : 32.03125 %
[2012-05-11 03:43:12,352] - [rest_client:770] INFO - rebalance percentage : 35.15625 %
[2012-05-11 03:43:14,355] - [rest_client:770] INFO - rebalance percentage : 38.28125 %
[2012-05-11 03:43:16,361] - [rest_client:770] INFO - rebalance percentage : 41.40625 %
[2012-05-11 03:43:18,365] - [rest_client:770] INFO - rebalance percentage : 44.53125 %
[2012-05-11 03:43:20,370] - [rest_client:770] INFO - rebalance percentage : 47.65625 %
[2012-05-11 03:43:22,410] - [rest_client:770] INFO - rebalance percentage : 51.5625 %
[2012-05-11 03:43:24,432] - [rest_client:770] INFO - rebalance percentage : 54.6875 %
[2012-05-11 03:43:26,436] - [rest_client:770] INFO - rebalance percentage : 62.5 %
[2012-05-11 03:43:28,459] - [rest_client:770] INFO - rebalance percentage : 71.875 %
[2012-05-11 03:43:30,469] - [rest_client:770] INFO - rebalance percentage : 81.25 %
[2012-05-11 03:43:32,477] - [rest_client:770] INFO - rebalance percentage : 89.0625 %
[2012-05-11 03:43:34,481] - [rest_client:770] INFO - rebalance percentage : 100.0 %
[2012-05-11 03:43:36,486] - [rest_client:770] INFO - rebalance percentage : 100.0 %
[2012-05-11 03:43:38,491] - [rest_client:770] INFO - rebalance percentage : 100.0 %
[2012-05-11 03:43:40,495] - [rest_client:770] INFO - rebalance percentage : 100.0 %
[2012-05-11 03:43:42,499] - [rest_client:770] INFO - rebalance percentage : 100.0 %
[2012-05-11 03:43:44,503] - [rest_client:770] INFO - rebalance percentage : 100.0 %
[2012-05-11 03:43:46,506] - [rest_client:763] ERROR -

{u'status': u'none', u'errorMessage': u'Rebalance failed. See logs for detailed reason. You can try rebalance again.'}

- rebalance failed
ERROR