Good question! Short answer is "I don't know". The follow-up question
that jumps to mind is whether or not <listBibl> was a member of
model.listLike back when it was stuck into the initial portion of the
content of <back>.
Either way, it looks to me like something that should be fixed in the
sense that <listBibl> should be allowed as a child of <back>, but I'm
not sure if the right fix is to put <listBibl> into model.listLike or
directly into model.frontPart. Either solution needs to be tested
quite thorougly, as there could easily be problematic consequences
(e.g., non-deterministic content models).
I'll try to poke at this a bit later this afternoon.
> I just came across the fact that listBibl is not valid as a child
> <back>. There is a bug report on this on SF
> https://sourceforge.net/p/tei/bugs/532/ but it seem that the fix
> misses <listBibl> since it is not part of model.listLike. Best,