Solr's prepareCommit doesn't set any commitData, and then when a commit is done, it's too late.
Here's a simple patch that adds the commit data during the prepareCommit command.
committed to 4x / trunk
Add unit test to TestReplicationHandler. This requires solrj support for prepareCommit, and thus includes that.
[branch_4x commit] Yonik Seeley
SOLR-3938: prepareCommit command omits commitData