Originally reported by @pbokoc:

In certain cases, a block element such as <table> or <figure> ends up being converted by docscii with a + preceding the element's ID. That seems to be valid ASCIIDoc (not 100% sure about that, but then again, who cares in unvalidated markup). The problem is that upon conversion back to docbook when running ccutil, these elements:

1. Get converted into their informal variants (table -> informaltable, figure -> informalfigure)
2. More importantly, they lose their IDs, so if there's a cross-reference pointing at such an element, the XML is invalid and the build fails.

I think the simplest way to fix this would be to make sure that any ID declaration is preceded by an empty newline. Experimenting on the Install Guide shows that this shouldn't break anything else - as it is right now, only a couple elements are converted with a + immediately before their IDs, and those are the ones that are failing, everything else is fine.