Program: 156563
Project: 156563
Buggy source:
@SideOnly(Side.CLIENT) @SubscribeEvent public void handleBlockHighlight(DrawBlockHighlightEvent e){
  if (e.target.typeOfHit == MovingObjectPosition.MovingObjectType.BLOCK) {
    int x=MathHelper.floor_double(e.target.hitVec.xCoord);
    int y=MathHelper.floor_double(e.target.hitVec.yCoord);
    int z=MathHelper.floor_double(e.target.hitVec.zCoord);
    BlockPos pos=new BlockPos(x,y,z);
    IBlockState state=e.player.worldObj.getBlockState(pos);
    Block block=state.getBlock();
    if (block instanceof ICustomHighlight) {
      AxisAlignedBB[] aabbs=((ICustomHighlight)block).getBoxes(e.player.worldObj,pos,state);
      Vec3 nPos=e.player.getPositionEyes(e.partialTicks).subtract(0,e.player.getEyeHeight(),0);
      long millis=System.currentTimeMillis();
      float expansion=(millis % 5000) / 2500F - 1;
      expansion*=Math.PI * 2;
      expansion=(MathHelper.sin(expansion) + 1) / 2;
      GL11.glEnable(GL11.GL_BLEND);
      OpenGlHelper.glBlendFunc(GL11.GL_SRC_ALPHA,GL11.GL_ONE_MINUS_SRC_ALPHA,GL11.GL_ONE,GL11.GL_ZERO);
      GL11.glColor4f(0.0F,0.0F,0.0F,0.4F);
      GL11.glLineWidth(2F);
      GL11.glDisable(GL11.GL_TEXTURE_2D);
      GL11.glDepthMask(false);
      double exp=((ICustomHighlight)block).getExpansion();
      exp+=expansion / 32D;
      nPos=nPos.subtract(x,y,z);
      for (      AxisAlignedBB aabb : aabbs) {
        AxisAlignedBB changed=aabb.expand(exp,exp,exp).offset(-nPos.xCoord,-nPos.yCoord,-nPos.zCoord);
        RenderGlobal.drawOutlinedBoundingBox(changed,-1);
      }
      GL11.glDepthMask(true);
      GL11.glEnable(GL11.GL_TEXTURE_2D);
      GL11.glDisable(GL11.GL_BLEND);
      e.setCanceled(true);
    }
  }
}

Fixed version (ground truth):
@SideOnly(Side.CLIENT) @SubscribeEvent public void handleBlockHighlight(DrawBlockHighlightEvent e){
  if (e.target.typeOfHit == MovingObjectPosition.MovingObjectType.BLOCK) {
    int x=MathHelper.floor_double(e.target.hitVec.xCoord);
    int y=MathHelper.floor_double(e.target.hitVec.yCoord);
    int z=MathHelper.floor_double(e.target.hitVec.zCoord);
    BlockPos pos=new BlockPos(x,y,z);
    IBlockState state=e.player.worldObj.getBlockState(pos);
    Block block=state.getBlock();
    if (block instanceof ICustomHighlight) {
      AxisAlignedBB[] aabbs=((ICustomHighlight)block).getBoxes(e.player.worldObj,pos,state);
      Vec3 nPos=e.player.getPositionEyes(e.partialTicks).subtract(0,e.player.getEyeHeight(),0);
      long millis=System.currentTimeMillis();
      float expansion=(millis % 5000) / 2500F - 1;
      expansion*=Math.PI * 2;
      expansion=(MathHelper.sin(expansion) + 1) / 2;
      expansion*=((ICustomHighlight)block).getBreathingCoefficent();
      GL11.glEnable(GL11.GL_BLEND);
      OpenGlHelper.glBlendFunc(GL11.GL_SRC_ALPHA,GL11.GL_ONE_MINUS_SRC_ALPHA,GL11.GL_ONE,GL11.GL_ZERO);
      GL11.glColor4f(0.0F,0.0F,0.0F,0.4F);
      GL11.glLineWidth(2F);
      GL11.glDisable(GL11.GL_TEXTURE_2D);
      GL11.glDepthMask(false);
      double exp=((ICustomHighlight)block).getExpansion();
      exp+=expansion / 32D;
      nPos=nPos.subtract(x,y,z);
      for (      AxisAlignedBB aabb : aabbs) {
        AxisAlignedBB changed=aabb.expand(exp,exp,exp).offset(-nPos.xCoord,-nPos.yCoord,-nPos.zCoord);
        RenderGlobal.drawOutlinedBoundingBox(changed,-1);
      }
      GL11.glDepthMask(true);
      GL11.glEnable(GL11.GL_TEXTURE_2D);
      GL11.glDisable(GL11.GL_BLEND);
      e.setCanceled(true);
    }
  }
}