The ATA is set at a certain measurement so that there's the right amount of load on the limbs in a "static" position. Anything under that recommeded ATA is going to add more load. Overload can show up as anything from cracked limbs, to shorter limb life, tuning issues, etc. I'd make sure the bow is set to spec.
Actually according to JoelC and Martin's website, there is a little more flexiblity than that, 1/4" shouldn't matter that much.