I've whittled down this problem to the attached document. The link is identical (copied/pasted from one location to the other). In the first instance it gets compiled correctly. In the second it doesn't. I can't figure out what, but it seems to be a bug, not user error. I've checked the XML code embedded in the document and it looks identical in both spots, and there are no extraneous characters between the opening [[ and the closing ]].
7624.Foo_test.docx
