I don't think its a bug, it is working the way they intended when they tweaked the AA system to get rid of the weapon requirements. But I don't think they had fully considered the effect on the ranged aspect of your AA line. So it may be an unintentional nerf.
Prior to the AA change, all the AA lines (at least for melee toons) were based on a specific weapon/shield. So in essence if you had AA lines with two different weapon requirements, the attack on one of those lines would be useless unless you constantaly switched out weapons during combat. After the change they dropped the weapon requirements so you would be free to use whichever skill you want, but the tradeoff was that those attack skills were put all on the same recharge timer.
I wonder if the shield skill timers are on the same recharge as the weapon skill timers.
I would suggest posting your issue on the SOE forums and maybe submitting an in-game bug report. The more voices they hear, the more likely they will be to fix your AA line back to the way that made the game more enjoyable for you.