Ive seen that happen only when the distance to the enemy is a bit bigger, for one reason or another so one extra AP is for "stepping closer".
Yeah, but during the final boss fight I noticed it happened. My character and the boss did not move a single step since the round before, but still my attacks were suddenly 5 AP instead of 4. Not just the first, all of them. And only for that character.
There might be effects in the game that increase AP cost or something, but if there are the game does not communicate that to the player, so I'm left feeling like this has to be a bug of some sort.
