Your example looks suspicious because you're calling _unset_embeddings and then install an embedding. That's explicitly warned against in the documentation.
What you're finding is that QQbar.convert_map_from(F) returns a broken map. That happens also if you don't try to register an embedding at allI think *that* needs fixing, and I don't think that has anything to do with coercions. In fact, if you install the embedding the way you're supposed to, the conversion seems to pick it up: sage: F.<b>=NumberField(a.minpoly(),embedding=a) sage: QQbar(b) == a True -- You received this message because you are subscribed to the Google Groups "sage-devel" group. To unsubscribe from this group and stop receiving emails from it, send an email to sage-devel+unsubscr...@googlegroups.com. To post to this group, send email to sage-devel@googlegroups.com. Visit this group at http://groups.google.com/group/sage-devel. For more options, visit https://groups.google.com/groups/opt_out.