I am running stock, unmodded and I am getting the exact same thing. First game was a reload of a 1.07 save, missed every time. I had one unit with 4 spell casters 15+ mana, INT no lower than 16, every single spell was a miss in four rounds of combat.
I started a new game, researched up to flame dart/lightning bolt. Exact same behavior with 14 INT on lvl 1 monsters.
I am using a custom sovereign, as are some of the posters above.