I concur with most of this: * does not seem to have anything to do with UND itself - may come up w/ UND because there are so many of 'em * probably occurs elsewhere, just not getting caught I am in the middle of ascertaining the paths to all of the <egXML>s in BACKLIST, in the hopes that if I locate the 8 problematic ones in there, something will jump out. Maybe we should talk tomorrow?
I've dug into this a bit now, and I'm finding a bunch of corner cases. There's not a single unifying cause, just cases where the ID generated for the correct source location don't match the ones generated for the bibliography, for different reasons. I'll look at it a bit more, but we may be better off just removing @source='UND' from the cases where it causes an error for now. We're seeing this in the epub because it actually attempts to validate all of its links.