I'm running a faction that has stealth (I've experienced this both with the pre-made and the custom one I'm using in the save), yet every now and then I still get attacked by monsters.  I've experienced this on both my computers, and I have provided a save game from either one.  I do get attacked less often, but the description says "Monsters won't attack this player's units".  So either Stealth isn't 100% working, or the description of it is inaccurate.  

I do know that other factions can attack me, but they're not.  It actually says "Monsters and Ruffians" over their portraits.

Because FE doesn't keep its random seed in the save game, you'll probably have to reload Stealth_Bug_2.EleSav a few times.  Just load the game up and end the turn, and maybe 1 in 5 times you'll get attacked by a monster.  If not, reload.  It seems like, if the monster doesn't attack you the first time, it's not going to until you reload.  For Stealth_Bug_1.EleSav, however, it happens every time.

http://darkseam.com/fe/Stealth_Bug_1.EleSav

http://darkseam.com/fe/Stealth_Bug_2.EleSav

I have no mods installed on either computer.