[Edi]

Zeldor, yes, that's correct.

Ich, I checked the Citadel of Pyriphlegeton locmask and it's correct. 16607 is an all-terrain-but-caves mask for a unique site, so your problem stems from the mapmaker mixing land and sea terrains in the same province, which should not be done.

I also just noticed your post about giving forts and no, it doesn't do that either in land or sea.