First of all, great mod! This is single-handedly ruining any chance of productivity I ever hoped to have in the evenings.
I noticed a few issues with the "Hidden Nationality" units in version 0.21a; specifically, I built the wonder that comes with "Deception" that allows all units created in one city to start with "Hidden Nationality". This is quite fun to do with heroes, but I digress
1. Units with "Hidden Nationality" can pillage in my borders, but cannot pillage in another nations borders. Is this intentional?
2. Units with "Hidden Nationality" cannot raze a city they have conquered (it makes sense that they can't claim the city, but can they also not raze cities?)
3. This one is tricky. If a stack of units (all with Hidden Nationality) conquer a city from another nation (say nation X) and fortify on it, any units from nation X can move onto the city without engaging in combat with the units with Hidden Nationality. Secondly, if you attempt to move another unit with Hidden Nationality and Marksmanship onto this stack (now containing both your units and a unit from nation X), Marksmanship will happily pick out one of your spellcasters over the unit from nation X and the units will engage in combat, even though the units are owned by you. As much fun as it is to level my Elven Assassins off of my Elven Adepts, this can get annoying as I have to check the square a stack is on for enemy units before attempting to add reinforcements.
Let me know if there is anything else I can do to help.