I'm having a problem casting spells on moving mobs. Basically, when they move even slightly out of my line of sight, my cast gets interrupted. It happened in the Garuda-egi fight on my SMN where the feathers were flying around in a circle and i died a few times (until i remembered Ruin II was insta-cast). But it also happened in Copperbell Hard on the 1st boss on my BLM. When the bomb comes hurtling along the walkway, i target it and start casting when it's by the last set of 3 blobs. But when it gets about halfway round, my cast fails and the party dies. All i can do is Scathe it.

I'm pretty sure it's something simple like toggling a setting, but i can't find it anywhere. Any help would be much appreciated