This is a problem brought about by medical rewrite. The full-auto is broken, often it happens that none of the hits does any damage to the target. Somehow, information packets are lost between the server and the final victim (your target).
It is better to use a semiauto, there is a greater probability that some intervention will be "real".
(I thought it is only a problem on WOG, where the FPS server is relatively small and unstable (see graphs on stats, where FPS jumps between ~ 12-35 FPS), but now on Thursday I saw the same situations on OFCRA where far fewer people and the FPS server are bigger and stable.)