It's more likely the Liberator is just so high or far that the shields aren't rendering to it. Shield not rendering = shots aren't stopped by it. There are cases where this doesn't apply, such as certain instances of client-side objects that spawn server-side objects, but, in general, what your client renders determines whether your shots hit it. There's also the ongoing "splash damage is not stopped by walls and shields" issue. That's one of the reasons they toned down explosives (and HE) in general in a previous GU.
