Mesh Part deforms without Weight painting being applied to it After parenting an armature with my mesh (using automatic weight), a part of it deforms when an unrelated bone moves even though that part of the mesh is not weight painted (its completely blue).

What could be the reason for this?

I have successfully rigged many models created by other people with no problems so maybe something is wrong with my model.
Select a vertex which has unwanted movement and check in the "N" properties panel which are its weights, then clear out the unwanted weights, even if they look "blue" in weight paint mode.