Aquatic units that are Flying without Flight are still penalised an extra 1AP per move. Aquatic states that movement costs 1 AP extra unless it is flying. So this is a bug. Seen when using Grant: Flight on a Razorfin Slider. In the same game the movement for a Shock Pomfret (with both Flying and Flight) was correctly costed.
I did some testing and it looks pretty inconsistent. In one game the following worked as expected (1AP movement costs): Grant: Flight (flying) from Tome of Arcanis on Glowing Slider (lumbering) Forced Evolution (aquatic) on opposing Crystal Dragon (arctic flight) Light as a Feather (flight) on Mirevixen (aquatic) Butterfly Wings (flying) on Mirevixen (aquatic) But this one didn't give correct movement costs: Butterfly Wings (flying) on Bloated Toad (lumbering). Moves cost 2 each.