The files in the slave's index is not removed even after they are removed from master.
The temp directories named index.xxxxxxx are not removed after use
The problem is that when we do a commit on the slave after replication is done. The commit does not re-open the IndexWriter. Therefore, the deletion policy does not take affect and older files are left as is. This can keep on building up. The only solution is to re-open the index writer.
A user has reported the issue http://markmail.org/thread/yw5n4dk2t5zbt5z5