From the spec, section 3.8:

The conversion of all basic types is supported except for the following: Id attributes (including the
attributes of embedded ids and derived identities), version attributes, relationship attributes, and
attributes explicitly annotated as Enumerated or Temporal or designated as such in the XML
descriptor.

EclipseLink is doing something non-standard. The silly thing is I actually had to add code to not apply these to Enumerated/Temporal attributes to "be spec compliant". Argh.