I've seen several variations of this bug, but this time I'm able to reproduce it reliably.  I load up the autosave and end the turn, and the army standing outside Tylan attacks it.  I have several Scouts stationed in that city, and none of them show up for the battle.  In fact, after my city gets taken, they all walk out of it.  

Save game below:
http://darkseam.com/fe/ScoutsNotDefending.EleSav

I did start this game after updating to 1.2.

Also, there was supposed to be one more scout,  but I ran into the autosave bug where any unit that finishes production that turn just goes missing. You can use this save to test that one out (you have to put the Scout back in the queue, and manually put it to the front).