Area of mesh moving along bone despite not being weight painted

Question

I have made a simple character model and am adding a skeleton to it, so i can use it as reference and so i can get a feel for how rigging and weight painting are.

The white box (Shoulder_L) has weight and is the one linked to the bone that's within it, however for some reason some vertices in the right arm move when i pose the shoulder, despite not having any weight.

(The area within the circle is where the vertex that moves is located)

Blend File

Answer 1

The right arm and shoulder have weights form Arm_L bone that are causing the deformation.

You can clearly see it when in vertex selection masking and adjusting weights levels in the Weight Tools panel.

To fix that problem set weights from Arm_L on the right shoulder and arm to 0, or use Subtract Brush on that areas.