I have noticed the same thing happening. It seems to fix if I slow down and not mash my macros/skills too much but I do think this should be tweaked because I think it definitely has an effect on the ability to heal, especially during times when there is a lot of aoe healing required + movement. It also seems to conveniently happen at the worst times, probably because its when the tank or a dps is near death that I end up trying to heal faster than the game can keep up with.