The optimization that allows opacity items that only contain one item (which can fold the opacity into it's own drawing) to flatten away will never apply when we have layer event region items. This is because opacity generates a stacking context and we always push a new layer event regions item for a stacking context. So if we want to keep this optimization we need to extend to to at least two items. Layer event regions items have empty bounds, which allows the non-overlapping test to pass for layer event region items. Although it will work with any non-overlapping items.