[Aleph]

Mictlan LA, due to its Atlantean heritage, is allowed to make underwater defense as per p. 124 of manual. However, it makes Atlantean Militia and land troops, instead of Atlantean Militia / Atlantean Shield Wielders / Atlantean Light Infantry, which is what should be there per p 124.

I'd also think that a nation supposedly capable of buying underwater PD should be able to make an underwater fortress where you could recruit the same kinds of units you buy for PD (and maybe even your heretofor capital only underwater sacred troops, although that might be a stretch). That, however, is an opinion. The fact that the PD in the game doesn't match up with the PD in the manual is a fact, and the fact that some units are Atlantean and others aren't makes me pretty sure it's a bug.

This was on the Cradle of Dominions map, if that makes any difference.