While looking into this report http://www.postgresql.org/message-id/CF48CCFB.65A9D%tim.kane@gmail.com I noticed that we don't accept empty values as xml "content" values, even though this should apparently be allowed by the spec. Attached is a patch to fix it (which needs updates to xml_1.out, which I omit here for simplicity).
The patch works, albeit must be applied with --ignore-whitespace. Attached the patch + xml_1.out updates.