[Edi]

That bug is a known issue and is related to a very complex bug involved in pretender creation, which requires a very specific set of conditions to manifest. The copy of the god appearing is a side effect of that, which also requires fairly specific conditions to manifest. It has been reported by PM a long time ago, but apparently all aspects of it have not been fixed. It was never shortlisted due to certain considerations regarding MP games where it could be abusable. It's too complex to easily do so without detailed instructions, which I'm obviously not going to provide to anyone.

Another related issue is the non-existent nations in the HoF, which is in the shortlist, but it is an indirect relation.

As far as diseases and healing afflictions go, see the FAQ.