Highlight Layer Doubling Indices, lowers FPS

Is it normal that a highlight layer would double the active indices, faces, and draw calls (but not mesh) in a scene when enabled? This dramatically lowers FPS.

I have a simple mouse over action controlling this turning on, and my mouseout is almost identical except I removeMesh instead of addMesh to the highlight layer.

function projectOnMouseOver(node: any){
            let targetUID = parseInt(pwtHelp.findTransformParent(node));
            let targetNode = pwt.nodes[targetUID].stage.stageRoot;
            let theChildren = targetNode.getChildMeshes(false, (mesh:any) => {
           //Filters out Instanced Meshes since they cause the highlight performance and console spam
                if(mesh.getClassName() === "Mesh"){
                    return true;
                }
                return false;
            })
            for(var child of theChildren){
                pwtControlActions.highlightLayer.addMesh(child, Color3.Blue());
            }
        }

It is expected to have more draw calls as meshes in the highlight layer will be drawn in a offline buffer in addition to their regular rendering.

However, a repro in the playground would help having a better view of the problem.