"Update existing nodes" does not update existing nodes. (feed import via LDAP query)

We are using:
Feeds 7.x-2.0-alpha7+18-dev
LDAP 7.x-2.0-beta2
to import and create nodes from an LDAP repository. Importing works fine. However, updating does not update nodes, as verified by: modify or delete the contents of one of the fields mapped to LDAP fields in a node. Use /import to import via LDAP query. Response:
"There are no new nodes."

This happens regardless of whether the Node Processor setting is "Update existing nodes" or "Update existing nodes only (Do not create new nodes)" and regardless of whether or not the "Skip hash check" box is checked or unchecked.