Nodes from map connectors (e.g., IMR) automatically get a UUID assigned to them by their connector. Something determines if the mode:uuid provided by the connector should be converted into a jcr:uuid exposed by referenceable nodes. However, when I create a node of type nt:versionLabels (which defines a residual reference property with a 'nt:version constraint), the mode:uuid field gets assigned the residual definition and falls into an infinite loop when it tries to validate the target of the reference (itself) against the nt:version constraint. IOW, part of materializing is to find definitions for properties and validate constraints, but in this case, validating the constraint causes the same node to be loaded from within its own materialize(...) call.