Some wierd thing happened regarding accuracy in a vs. I played. I was on one of my custom maps (a very tight map where the whole floor is ice) when suddenly, amidst the chaos, my base accuracy was 80% (75/70% for the Barudits/Rogues) for most of my attacks (never-miss attacks still succeeded). I can confirm that the attacking units weren't blinded.
Were they standing on ice tiles?
Yes they were - is that the reason?
Yup! If you pull up space info for ice tiles, you should see that they impose an accuracy penalty.