Making an item private does not remove it from the (Solr) OAI index with incremental indexing(./dspace oai import without -c). Since in XOAI.java, findInArchiveOrWithdrawnDiscoverableModifiedSince() is used to find changed items, and since this method excludes items which have been made private, those items are not considered for an update.
I'm not sure about how this should be handled in order to conform to OAI standards. Should a private item be handled like a withdrawn item (delete flag and no metadata)? Should it be removed completely?