Somewhere between when I tried Vangelis's patch (earlier in this
thread) and when it was installed, it seems that a further change was
made to preview-region that breaks previews in indirect buffers.
Specifically, the substitution buffer-file-name ->
(TeX-buffer-file-name) was applied where it shouldn't be.

The issue is as explained in my earlier email in this thread -- we
actually want "<none>" to be the filename when doing previews for
indirect buffers, so that preview-parse-messages ultimately places
them according to the command buffer rather than according to the
filename.  (It might clarify here to note that AFAIK, the "original"
argument to TeX-region-create is relevant only when doing
preview-document, which is irrelevant for indirect buffers.)

I've attached a patch reverting this particular substitution, so that
previews once again work in indirect buffers.

Thanks, best,

Paul