I noticed something similar, so far only with Cool VL Viewer. I don't think it is related to impostor settings.
To me it happens when I am at a crowded place with lots of mesh avatars. Some of my body parts appear doubled or even tripled when moving or moving the cam around. Strangely it is only my own (mesh) body and hair that it happens to. The other avatars look okay.
It is like an artifact / refreshing issue. I can try to gather further information, if needed.