And lets make it second bug report:
https://playcanvas.com/project/1215543/overview/breaking-the-rig
ANIM_LAYER_ADDITIVE
Anim component additive layer mode does not work correctly if anim component is not on entity with Render component. If Anim component is on different entity than Render component, then animations in same Base layer works correctly, but if you add another layer and set blend type to additive weird scaling behavior happens:
Same behavior happens if you do it over editor or doing everything via code.