[1.8.8] Model not copying player rotation when sneaking

So, my model that I am rendering on the player's back works quite fine. But, my only problem is that when the player sneaks, my model doesn't rotate. Here's an example:

Standing with model:

Sneaking with model:

Here's my model code:

package com.happykiller.weightlimit.render.models;

import net.minecraft.client.model.ModelBiped;
import net.minecraft.client.model.ModelRenderer;
import net.minecraft.entity.Entity;

public class ModelSmallBackpack extends ModelBiped {
    ModelRenderer BackpackBase;
    ModelRenderer BackpackSecondary;
    ModelRenderer MainButton;
    ModelRenderer PocketLeft;
    ModelRenderer PocketRight;
    ModelRenderer PocketFront;
    ModelRenderer FrontButton;
  
    public ModelSmallBackpack(float scale) {
    	super(scale, 0.0F, 64, 32);
    	
    	BackpackBase = new ModelRenderer(this, 0, 0);
    	BackpackBase.addBox(-3F, 1F, 2F, 6, 8, 2);
    	BackpackBase.setRotationPoint(0F, 0F, 0F);
    	BackpackBase.setTextureSize(64, 32);
    	BackpackBase.mirror = true;
    setRotation(BackpackBase, 0F, 0F, 0F);
    
    BackpackSecondary = new ModelRenderer(this, 16, 0);
    BackpackSecondary.addBox(-2F, 3F, 3.5F, 4, 6, 1);
    BackpackSecondary.setRotationPoint(0F, 0F, 0F);
    BackpackSecondary.setTextureSize(64, 32);
    BackpackSecondary.mirror = true;
    setRotation(BackpackSecondary, 0F, 0F, 0F);
    
    MainButton = new ModelRenderer(this, 0, 10);
    MainButton.addBox(-1F, 1.5F, 3.2F, 2, 1, 1);
    MainButton.setRotationPoint(0F, 0F, 0F);
    MainButton.setTextureSize(64, 32);
    MainButton.mirror = true;
    setRotation(MainButton, 0F, 0F, 0F);
    
    PocketLeft = new ModelRenderer(this, 0, 12);
    PocketLeft.addBox(2.5F, 6F, 1.8F, 1, 2, 2);
    PocketLeft.setRotationPoint(0F, 0F, 0F);
    PocketLeft.setTextureSize(64, 32);
    PocketLeft.mirror = true;
    setRotation(PocketLeft, 0F, 0F, 0F);
    
    PocketRight = new ModelRenderer(this, 6, 12);
    PocketRight.addBox(-3.533333F, 6F, 1.8F, 1, 2, 2);
    PocketRight.setRotationPoint(0F, 0F, 0F);
    PocketRight.setTextureSize(64, 32);
    PocketRight.mirror = true;
    setRotation(PocketRight, 0F, 0F, 0F);
    
    PocketFront = new ModelRenderer(this, 0, 16);
    PocketFront.addBox(-1F, 6F, 4F, 2, 2, 1);
    PocketFront.setRotationPoint(0F, 0F, 0F);
    PocketFront.setTextureSize(64, 32);
    PocketFront.mirror = true;
    setRotation(PocketFront, 0F, 0F, 0F);
    
    FrontButton = new ModelRenderer(this, 0, 10);
    FrontButton.addBox(-1F, 5F, 3.8F, 2, 1, 1);
    FrontButton.setRotationPoint(0F, 0F, 0F);
    FrontButton.setTextureSize(64, 32);
    FrontButton.mirror = true;
    setRotation(FrontButton, 0F, 0F, 0F);
  }
  
  public void render(Entity entity, float f, float f1, float f2, float f3, float f4, float f5) {
  setRotationAngles(f, f1, f2, f3, f4, f5, entity);
  
  BackpackBase.render(f5);
  BackpackSecondary.render(f5);
  MainButton.render(f5);
  PocketLeft.render(f5);
  PocketRight.render(f5);
  PocketFront.render(f5);
  FrontButton.render(f5);
  }
  
  private void setRotation(ModelRenderer model, float x, float y, float z) {
  model.rotateAngleX = x;
  model.rotateAngleY = y;
  model.rotateAngleZ = z;
  }
  
  public void setRotationAngles(float f, float f1, float f2, float f3, float f4, float f5, Entity entity) {
  super.setRotationAngles(f, f1, f2, f3, f4, f5, entity);
  
  //Is this the problem?
  
  copyModelAngles(this.bipedBody, BackpackBase);
  copyModelAngles(this.bipedBody, BackpackSecondary);
  copyModelAngles(this.bipedBody, MainButton);
  copyModelAngles(this.bipedBody, PocketLeft);
  copyModelAngles(this.bipedBody, PocketRight);
  copyModelAngles(this.bipedBody, PocketFront);
  copyModelAngles(this.bipedBody, FrontButton);
  }
}

I thought #copyModelAngles() would do it, but it doesn't help. Am I calling it incorrectly?